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sched.go
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sched.go
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package server
import (
"context"
"errors"
"fmt"
"log/slog"
"reflect"
"runtime"
"slices"
"sort"
"strings"
"sync"
"time"
"github.com/ollama/ollama/api"
"github.com/ollama/ollama/envconfig"
"github.com/ollama/ollama/format"
"github.com/ollama/ollama/gpu"
"github.com/ollama/ollama/llm"
)
type LlmRequest struct {
ctx context.Context //nolint:containedctx
model *Model
opts api.Options
sessionDuration time.Duration
successCh chan *runnerRef
errCh chan error
}
type Scheduler struct {
pendingReqCh chan *LlmRequest
finishedReqCh chan *LlmRequest
expiredCh chan *runnerRef
unloadedCh chan interface{}
loaded map[string]*runnerRef
loadedMu sync.Mutex
loadFn func(req *LlmRequest, ggml *llm.GGML, gpus gpu.GpuInfoList)
newServerFn func(gpus gpu.GpuInfoList, model string, ggml *llm.GGML, adapters []string, projectors []string, opts api.Options) (llm.LlamaServer, error)
getGpuFn func() gpu.GpuInfoList
}
var ErrMaxQueue = fmt.Errorf("server busy, please try again. maximum pending requests exceeded")
func InitScheduler(ctx context.Context) *Scheduler {
sched := &Scheduler{
pendingReqCh: make(chan *LlmRequest, envconfig.MaxQueuedRequests),
finishedReqCh: make(chan *LlmRequest, envconfig.MaxQueuedRequests),
expiredCh: make(chan *runnerRef, envconfig.MaxQueuedRequests),
unloadedCh: make(chan interface{}, envconfig.MaxQueuedRequests),
loaded: make(map[string]*runnerRef),
newServerFn: llm.NewLlamaServer,
getGpuFn: gpu.GetGPUInfo,
}
sched.loadFn = sched.load
return sched
}
// context must be canceled to decrement ref count and release the runner
func (s *Scheduler) GetRunner(c context.Context, model *Model, opts api.Options, sessionDuration time.Duration) (chan *runnerRef, chan error) {
// allocate a large enough kv cache for all parallel requests
if opts.NumCtx < 4 {
opts.NumCtx = 4
}
opts.NumCtx *= envconfig.NumParallel
req := &LlmRequest{
ctx: c,
model: model,
opts: opts,
sessionDuration: sessionDuration,
successCh: make(chan *runnerRef),
errCh: make(chan error, 1),
}
select {
case s.pendingReqCh <- req:
default:
req.errCh <- ErrMaxQueue
}
return req.successCh, req.errCh
}
// Returns immediately, spawns go routines for the scheduler which will shutdown when ctx is done
func (s *Scheduler) Run(ctx context.Context) {
slog.Debug("starting llm scheduler")
go func() {
s.processPending(ctx)
}()
go func() {
s.processCompleted(ctx)
}()
}
func (s *Scheduler) processPending(ctx context.Context) {
for {
select {
case <-ctx.Done():
slog.Debug("shutting down scheduler pending loop")
return
case pending := <-s.pendingReqCh:
// Block other requests until we get this pending request running
if pending.ctx.Err() != nil {
slog.Debug("pending request cancelled or timed out, skipping scheduling")
continue
}
for {
var runnerToExpire *runnerRef
s.loadedMu.Lock()
runner := s.loaded[pending.model.ModelPath]
loadedCount := len(s.loaded)
s.loadedMu.Unlock()
if runner != nil {
if runner.needsReload(ctx, pending) {
runnerToExpire = runner
} else {
// Runner is usable, return it
pending.useLoadedRunner(runner, s.finishedReqCh)
break
}
} else if envconfig.MaxRunners > 0 && loadedCount >= envconfig.MaxRunners {
slog.Debug("max runners achieved, unloading one to make room", "runner_count", loadedCount)
runnerToExpire = s.findRunnerToUnload()
} else {
// Either no models are loaded or below envconfig.MaxRunners
// Get a refreshed GPU list
gpus := s.getGpuFn()
// Load model for fitting
ggml, err := llm.LoadModel(pending.model.ModelPath)
if err != nil {
pending.errCh <- err
break
}
// If we're CPU only mode, just limit by envconfig.MaxRunners above
// TODO handle system memory exhaustion
if (len(gpus) == 1 && gpus[0].Library == "cpu") || pending.opts.NumGPU == 0 {
slog.Debug("cpu mode with existing models, loading")
s.loadFn(pending, ggml, gpus)
break
}
// No models loaded. Load the model but prefer the best fit.
if loadedCount == 0 {
slog.Debug("loading first model", "model", pending.model.ModelPath)
g := pickBestFitGPUs(pending, ggml, gpus)
if g != nil {
gpus = g
}
s.loadFn(pending, ggml, gpus)
break
}
// More than one loaded model, so we have to see if the new one fits
// Update free memory from currently loaded models
s.updateFreeSpace(gpus)
gpus = pickBestFitGPUs(pending, ggml, gpus)
if gpus != nil {
slog.Debug("new model fits with existing models, loading")
s.loadFn(pending, ggml, gpus)
break
}
runnerToExpire = s.findRunnerToUnload()
}
if runnerToExpire == nil {
// Shouildn't happen
slog.Error("runner to expire was nil!")
continue
}
// Trigger an expiration to unload once it's done
runnerToExpire.refMu.Lock()
slog.Debug("resetting model to expire immediately to make room", "modelPath", runnerToExpire.modelPath, "refCount", runnerToExpire.refCount)
if runnerToExpire.expireTimer != nil {
runnerToExpire.expireTimer.Stop()
runnerToExpire.expireTimer = nil
}
runnerToExpire.sessionDuration = 0
if runnerToExpire.refCount <= 0 {
s.expiredCh <- runnerToExpire
}
runnerToExpire.refMu.Unlock()
// Wait for the unload to happen
// Note: at this point we're queueing up all incoming requests, even if they were for
// a different model that's loaded and not scheduled to be removed.
slog.Debug("waiting for pending requests to complete and unload to occur", "modelPath", runnerToExpire.modelPath)
select {
case <-ctx.Done():
slog.Debug("shutting down scheduler pending loop")
return
case <-s.unloadedCh:
slog.Debug("unload completed", "modelPath", runnerToExpire.modelPath)
continue
}
}
case <-s.unloadedCh:
// An unload request when there are no pending request can be ignored
slog.Debug("ignoring unload event with no pending requests")
}
}
}
func (s *Scheduler) processCompleted(ctx context.Context) {
// Process completed requests, expired timers, and unloading models
for {
select {
case <-ctx.Done():
slog.Debug("shutting down scheduler completed loop")
return
case finished := <-s.finishedReqCh:
s.loadedMu.Lock()
runner := s.loaded[finished.model.ModelPath]
s.loadedMu.Unlock()
if runner == nil {
slog.Error("finished request signal received after model unloaded", "modelPath", finished.model.ModelPath)
continue
}
runner.refMu.Lock()
runner.refCount--
if runner.refCount <= 0 {
if runner.sessionDuration <= 0 {
slog.Debug("runner with zero duration has gone idle, expiring to unload", "modelPath", runner.modelPath)
if runner.expireTimer != nil {
runner.expireTimer.Stop()
runner.expireTimer = nil
}
s.expiredCh <- runner
} else if runner.expireTimer == nil {
slog.Debug("runner with non-zero duration has gone idle, adding timer", "modelPath", runner.modelPath, "duration", runner.sessionDuration)
runner.expireTimer = time.AfterFunc(runner.sessionDuration, func() {
slog.Debug("timer expired, expiring to unload", "modelPath", runner.modelPath)
runner.refMu.Lock()
defer runner.refMu.Unlock()
if runner.expireTimer != nil {
runner.expireTimer.Stop()
runner.expireTimer = nil
}
s.expiredCh <- runner
})
runner.expiresAt = time.Now().Add(runner.sessionDuration)
} else {
slog.Debug("runner with non-zero duration has gone idle, resetting timer", "modelPath", runner.modelPath, "duration", runner.sessionDuration)
runner.expireTimer.Reset(runner.sessionDuration)
runner.expiresAt = time.Now().Add(runner.sessionDuration)
}
}
slog.Debug("after processing request finished event", "modelPath", runner.modelPath, "refCount", runner.refCount)
runner.refMu.Unlock()
case runner := <-s.expiredCh:
slog.Debug("runner expired event received", "modelPath", runner.modelPath)
runner.refMu.Lock()
if runner.refCount > 0 {
// Shouldn't happen, but safeguard to ensure no leaked runners
slog.Debug("expired event with positive ref count, retrying", "modelPath", runner.modelPath, "refCount", runner.refCount)
go func(runner *runnerRef) {
// We can't unload yet, but want to as soon as the current request completes
// So queue up another expired event
time.Sleep(10 * time.Millisecond)
s.expiredCh <- runner
}(runner)
runner.refMu.Unlock()
continue
}
s.loadedMu.Lock()
slog.Debug("got lock to unload", "modelPath", runner.modelPath)
finished := runner.waitForVRAMRecovery()
runner.unload()
delete(s.loaded, runner.modelPath)
s.loadedMu.Unlock()
slog.Debug("runner released", "modelPath", runner.modelPath)
runner.refMu.Unlock()
<-finished
slog.Debug("sending an unloaded event", "modelPath", runner.modelPath)
s.unloadedCh <- struct{}{}
}
}
}
// Complete the pending request and send the runner back to the requester
// Wires up a finished event after the request context is completed
// Updates session duration, and resets expiration timer
func (pending *LlmRequest) useLoadedRunner(runner *runnerRef, finished chan *LlmRequest) {
runner.refMu.Lock()
defer runner.refMu.Unlock()
runner.refCount++
if runner.expireTimer != nil {
runner.expireTimer.Stop()
runner.expireTimer = nil
}
runner.sessionDuration = pending.sessionDuration
pending.successCh <- runner
go func() {
<-pending.ctx.Done()
slog.Debug("context for request finished")
finished <- pending
}()
}
func (s *Scheduler) load(req *LlmRequest, ggml *llm.GGML, gpus gpu.GpuInfoList) {
llama, err := s.newServerFn(gpus, req.model.ModelPath, ggml, req.model.AdapterPaths, req.model.ProjectorPaths, req.opts)
if err != nil {
// some older models are not compatible with newer versions of llama.cpp
// show a generalized compatibility error until there is a better way to
// check for model compatibility
if errors.Is(llm.ErrUnsupportedFormat, err) || strings.Contains(err.Error(), "failed to load model") {
err = fmt.Errorf("%v: this model may be incompatible with your version of Ollama. If you previously pulled this model, try updating it by running `ollama pull %s`", err, req.model.ShortName)
}
slog.Info("NewLlamaServer failed", "model", req.model.ModelPath, "error", err)
req.errCh <- err
return
}
runner := &runnerRef{
model: req.model,
modelPath: req.model.ModelPath,
llama: llama,
Options: &req.opts,
sessionDuration: req.sessionDuration,
gpus: gpus,
estimatedVRAM: llama.EstimatedVRAM(),
estimatedTotal: llama.EstimatedTotal(),
loading: true,
refCount: 1,
}
runner.refMu.Lock()
s.loadedMu.Lock()
s.loaded[req.model.ModelPath] = runner
slog.Info("loaded runners", "count", len(s.loaded))
s.loadedMu.Unlock()
go func() {
defer runner.refMu.Unlock()
if err = llama.WaitUntilRunning(req.ctx); err != nil {
slog.Error("error loading llama server", "error", err)
runner.refCount--
req.errCh <- err
slog.Debug("triggering expiration for failed load", "model", runner.modelPath)
s.expiredCh <- runner
return
}
slog.Debug("finished setting up runner", "model", req.model.ModelPath)
runner.loading = false
go func() {
<-req.ctx.Done()
slog.Debug("context for request finished")
s.finishedReqCh <- req
}()
req.successCh <- runner
}()
}
func (s *Scheduler) updateFreeSpace(allGpus gpu.GpuInfoList) {
type predKey struct {
Library string
ID string
}
predMap := map[predKey]uint64{} // Sum up the total predicted usage per GPU for all runners
s.loadedMu.Lock()
for _, r := range s.loaded {
r.refMu.Lock()
gpuIDs := make([]string, 0, len(r.gpus))
if r.llama != nil {
// TODO this should be broken down by GPU instead of assuming uniform spread
estimatedVRAMPerGPU := r.llama.EstimatedVRAM() / uint64(len(r.gpus))
for _, gpu := range r.gpus {
gpuIDs = append(gpuIDs, gpu.ID)
}
for _, gpu := range allGpus {
if slices.Contains(gpuIDs, gpu.ID) {
predMap[predKey{gpu.Library, gpu.ID}] += estimatedVRAMPerGPU
}
}
} else {
slog.Warn("unexpected nil runner reference, memory prediction may be incorrect")
}
r.refMu.Unlock()
}
s.loadedMu.Unlock()
// Now that we've summed up all the GPU usage predictions across all the loaded runners, update the gpu list
for i := range allGpus {
if p, ok := predMap[predKey{allGpus[i].Library, allGpus[i].ID}]; ok {
slog.Debug("gpu reported", "gpu", allGpus[i].ID, "library", allGpus[i].Library, "available", format.HumanBytes2(allGpus[i].FreeMemory))
if p > allGpus[i].TotalMemory {
// Shouldn't happen
slog.Warn("predicted usage exceeds VRAM", "gpu", allGpus[i].ID, "totalMemory", allGpus[i].TotalMemory, "predicted", p)
allGpus[i].FreeMemory = 0
} else if (allGpus[i].TotalMemory - p) < allGpus[i].FreeMemory { // predicted free is smaller than reported free, use it
// TODO maybe we should just always trust our numbers, since cuda's free memory reporting is laggy
// and we might unload models we didn't actually need to. The risk is if some other GPU intensive app is loaded
// after we start our first runner, then we'll never acount for that, so picking the smallest free value seems prudent.
allGpus[i].FreeMemory = allGpus[i].TotalMemory - p
}
slog.Info("updated VRAM", "gpu", allGpus[i].ID, "library", allGpus[i].Library, "total", format.HumanBytes2(allGpus[i].TotalMemory), "available", format.HumanBytes2(allGpus[i].FreeMemory))
}
}
}
type runnerRef struct {
refMu sync.Mutex
// refCond sync.Cond // Signaled on transition from 1 -> 0 refCount
refCount uint // prevent unloading if > 0
// unloading bool // set to true when we are trying to unload the runner
llama llm.LlamaServer
loading bool // True only during initial load, then false forever
gpus gpu.GpuInfoList // Recorded at time of provisioning
estimatedVRAM uint64
estimatedTotal uint64
sessionDuration time.Duration
expireTimer *time.Timer
expiresAt time.Time
model *Model
modelPath string
*api.Options
}
// The refMu must already be held when calling unload
func (runner *runnerRef) unload() {
if runner.expireTimer != nil {
runner.expireTimer.Stop()
runner.expireTimer = nil
}
if runner.llama != nil {
runner.llama.Close()
}
runner.model = nil
runner.llama = nil
runner.Options = nil
runner.gpus = nil
}
func (runner *runnerRef) needsReload(ctx context.Context, req *LlmRequest) bool {
slog.Debug("evaluating already loaded", "model", req.model.ModelPath)
runner.refMu.Lock()
defer runner.refMu.Unlock()
timeout := 10 * time.Second
if runner.loading {
timeout = 2 * time.Minute // Initial load can take a long time for big models on slow systems...
}
if runner.Options == nil {
return true
}
// Don't reload runner if num_gpu=-1 was provided
optsExisting := runner.Options.Runner
optsNew := req.opts.Runner
if optsNew.NumGPU < 0 {
optsExisting.NumGPU = -1
optsNew.NumGPU = -1
}
ctx, cancel := context.WithTimeout(ctx, timeout)
defer cancel()
if !reflect.DeepEqual(runner.model.AdapterPaths, req.model.AdapterPaths) || // have the adapters changed?
!reflect.DeepEqual(runner.model.ProjectorPaths, req.model.ProjectorPaths) || // have the projectors changed?
!reflect.DeepEqual(optsExisting, optsNew) || // have the runner options changed?
runner.llama.Ping(ctx) != nil {
return true
}
return false
}
// Free memory reporting on GPUs can lag for a while even after the runner
// exits, so we have to keep checking until we see the available memory recover,
// otherwise subsequent model loads will get far less layers loaded or worse
// case, may completely fall back to CPU mode.
// This routine must be called before the runner unloads so it can establish
// a before and after GPU memory allocation. The returned channel
// will be notified when we're done waiting, or have timed out and should
// proceed anyway
func (runner *runnerRef) waitForVRAMRecovery() chan interface{} {
finished := make(chan interface{}, 1)
// CPU or Metal don't need checking, so no waiting required, windows can page VRAM, and the APIs we query tend to be optimistic on free space
if (len(runner.gpus) == 1 && (runner.gpus[0].Library == "cpu" || runner.gpus[0].Library == "metal")) || runtime.GOOS == "windows" {
finished <- struct{}{}
return finished
}
start := time.Now()
// Establish a baseline before we unload
gpusBefore := gpu.GetGPUInfo()
var totalMemoryBefore, freeMemoryBefore uint64
for _, gpu := range gpusBefore {
totalMemoryBefore += gpu.TotalMemory
freeMemoryBefore += gpu.FreeMemory
}
go func() {
expiresAt := start.Add(5 * time.Second) // typical convergence is 0.5-1.5s
ticker := time.NewTicker(250 * time.Millisecond)
defer ticker.Stop()
for {
<-ticker.C
if time.Now().After(expiresAt) {
slog.Warn("gpu VRAM usage didn't recover within timeout", "seconds", time.Since(start).Seconds())
finished <- struct{}{}
}
// Query GPUs, look for free to go back up
gpusNow := gpu.GetGPUInfo()
var totalMemoryNow, freeMemoryNow uint64
for _, gpu := range gpusNow {
totalMemoryNow += gpu.TotalMemory
freeMemoryNow += gpu.FreeMemory
}
// If we're within ~80% of the estimated memory usage recovered, bail out
if float32(freeMemoryNow-freeMemoryBefore) > float32(runner.estimatedVRAM)*0.8 {
slog.Debug(fmt.Sprintf("gpu VRAM free memory converged after %0.2f seconds", time.Since(start).Seconds()))
finished <- struct{}{}
return
}
}
}()
return finished
}
type ByDuration []*runnerRef
func (a ByDuration) Len() int { return len(a) }
func (a ByDuration) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
func (a ByDuration) Less(i, j int) bool {
// uint64 to turn negative time (never unload) to largest
return uint64(a[i].sessionDuration) < uint64(a[j].sessionDuration)
}
// TODO - future consideration to pick runners based on size
// type BySize []*runnerRef
// func (a BySize) Len() int { return len(a) }
// func (a BySize) Swap(i, j int) { a[i], a[j] = a[j], a[i] }
// func (a BySize) Less(i, j int) bool { return a[i].estimatedVRAM < a[j].estimatedVRAM }
// pickBestFitGPUs will try to find the optimal placement of the model in the available GPUs where the model fully fits
// If the model can not be fit fully within the available GPU(s) nil is returned
func pickBestFitGPUs(req *LlmRequest, ggml *llm.GGML, gpus gpu.GpuInfoList) gpu.GpuInfoList {
var estimatedVRAM uint64
for _, gl := range gpus.ByLibrary() {
var ok bool
sgl := append(make(gpu.GpuInfoList, 0, len(gl)), gl...)
// TODO - potentially sort by performance capability, existing models loaded, etc.
// Note: at present, this will favor more VRAM over faster GPU speed in mixed setups
sort.Sort(sort.Reverse(gpu.ByFreeMemory(sgl)))
// First attempt to fit the model into a single GPU
for _, g := range sgl {
if ok, estimatedVRAM = llm.PredictServerFit([]gpu.GpuInfo{g}, ggml, req.model.AdapterPaths, req.model.ProjectorPaths, req.opts); ok {
slog.Debug("new model will fit in available VRAM in single GPU, loading", "model", req.model.ModelPath, "gpu", g.ID, "available", g.FreeMemory, "required", format.HumanBytes2(estimatedVRAM))
return []gpu.GpuInfo{g}
}
}
// TODO future refinements
// - if multiple Libraries, see if any single GPU in any Library will fit
// - try subsets of GPUs instead of just falling back to 1 or all in a family
// Now try all the GPUs
if ok, estimatedVRAM = llm.PredictServerFit(sgl, ggml, req.model.AdapterPaths, req.model.ProjectorPaths, req.opts); ok {
slog.Debug("new model will fit in available VRAM, loading", "model", req.model.ModelPath, "library", sgl[0].Library, "required", format.HumanBytes2(estimatedVRAM))
return sgl
}
}
return nil
}
// findRunnerToUnload finds a runner to unload to make room for a new model
func (s *Scheduler) findRunnerToUnload() *runnerRef {
s.loadedMu.Lock()
runnerList := make([]*runnerRef, 0, len(s.loaded))
for _, r := range s.loaded {
runnerList = append(runnerList, r)
}
s.loadedMu.Unlock()
// In the future we can enhance the algorithm to be smarter about picking the optimal runner to unload
// e.g., if we have multiple options, will one make room for the request?
sort.Sort(ByDuration(runnerList))
// First try to find a runner that's already idle
for _, runner := range runnerList {
runner.refMu.Lock()
rc := runner.refCount
runner.refMu.Unlock()
if rc == 0 {
slog.Debug("found an idle runner to unload")
return runner
}
}
// None appear idle, just wait for the one with the shortest duration
slog.Debug("no idle runners, picking the shortest duration", "count", len(runnerList))
return runnerList[0]
}
func (s *Scheduler) unloadAllRunners() {
s.loadedMu.Lock()
defer s.loadedMu.Unlock()
for model, runner := range s.loaded {
if runner.llama != nil {
slog.Debug("shutting down runner", "model", model)
runner.llama.Close()
}
}
}