Scheduling policy switching

cnf/make.conf.example

@@ -291,6 +291,23 @@
 #     unset.
 #PORTAGE_IONICE_COMMAND="ionice -c 3 -p \${PID}"
 #
+# PORTAGE_SCHEDULING_POLICY allows changing the current scheduling policy. The
+# supported options are 'other', 'batch', 'idle', 'fifo' and 'round-robin'. When
+# unset, the scheduling policy remains unchanged, by default Linux uses 'other'
+# policy. Users that wish to minimize the Portage's impact on system
+# responsiveness should set scheduling policy to 'idle' which significantly
+# reduces the disruption to the rest of the system by scheduling Portage as
+# extremely low priority processes.
+#
+#PORTAGE_SCHEDULING_POLICY="idle"
+#
+# PORTAGE_SCHEDULING_PRIORITY allows changing the priority (1-99) of the current
+# scheduling policy, only applies if PORTAGE_SCHEDULING_POLICY is set to 'fifo'
+# or 'round-robin', for others the only supported priority is 0, If unset,
+# defaults to lowest priority of the selected scheduling policy.
+#
+#PORTAGE_SCHEDULING_PRIORITY="99"
+#
 # AUTOCLEAN enables portage to automatically clean out older or overlapping
 #     packages from the system after every successful merge. This is the
 #     same as running 'emerge -c' after every merge. Set with: "yes" or "no".

lib/_emerge/actions.py

@@ -3054,6 +3054,7 @@ def config_protect_check(trees):
 def apply_priorities(settings):
     ionice(settings)
     nice(settings)
+    set_scheduling_policy(settings)
 
 
 def nice(settings):
@@ -3094,6 +3095,50 @@ def ionice(settings):
         )
 
 
+def set_scheduling_policy(settings):
+    scheduling_policy = settings.get("PORTAGE_SCHEDULING_POLICY")
+    scheduling_priority = settings.get("PORTAGE_SCHEDULING_PRIORITY")
+
+    if platform.system() != "Linux" or not scheduling_policy:
+        return os.EX_OK
+
+    policies = {
+        "other": os.SCHED_OTHER,
+        "batch": os.SCHED_BATCH,
+        "idle": os.SCHED_IDLE,
+        "fifo": os.SCHED_FIFO,
+        "round-robin": os.SCHED_RR,
+    }
+
+    out = portage.output.EOutput()
+
+    if scheduling_policy in policies:
+        policy = policies[scheduling_policy]
+    else:
+        out.eerror("Invalid policy in PORTAGE_SCHEDULING_POLICY.")
+        out.eerror(
+            "See the make.conf(5) man page for PORTAGE_SCHEDULING_POLICY usage instructions."
+        )
+        return os.EX_USAGE
+
+    if not scheduling_priority:
+        scheduling_priority = os.sched_get_priority_min(policy)
+    else:
+        scheduling_priority = int(scheduling_priority)
+        if scheduling_priority not in range(
+            os.sched_get_priority_min(policy), os.sched_get_priority_max(policy) + 1
+        ):
+            out.eerror("Invalid priority in PORTAGE_SCHEDULING_PRIORITY.")
+            out.eerror(
+                "See the make.conf(5) man page for PORTAGE_SCHEDULING_PRIORITY usage instructions."
+            )
+            return os.EX_USAGE
+
+    os.sched_setscheduler(portage.getpid(), policy, os.sched_param(scheduling_priority))
+
+    return os.EX_OK
+
+
 def setconfig_fallback(root_config):
     setconfig = root_config.setconfig
     setconfig._create_default_config()

man/make.conf.5

@@ -1080,6 +1080,22 @@ will set idle io priority. For more information about ionice, see
 Portage will also set the autogroup-nice value (see fBsched\fR(7))), if
 FEATURES="pid\-sandbox" is enabled.
 .TP
+\fBPORTAGE_SCHEDULING_POLICY\fR = \fI[policy name]\fR
+Allows changing the current scheduling policy. The supported options are
+\fBother\fR, \fBbatch\fR, \fBidle\fR, \fBfifo\fR, and \fBround-robin\fR. When
+unset, the scheduling policy remains unchanged, by default Linux uses 'other'
+policy. Users that wish to minimize the Portage's impact on system
+responsiveness should set scheduling policy to \fBidle\fR, which significantly
+reduces the disruption to the rest of the system by scheduling Portage as
+extremely low priority processes. see \fBsched\fR(7) for more information.
+.TP
+\fBPORTAGE_SCHEDULING_PRIORITY\fR = \fI[priority]\fR
+Allows changing the priority (1-99) of the current scheduling policy, only
+applies if PORTAGE _SCHEDULING_POLICY is set to 'fifo' or 'round-robin',
+for others the only supported priority is 0, If unset, defaults to lowest
+priority of the selected scheduling policy. For more information about
+scheduler, see \fBsched\fR(7). This variable is unset by default.
+.TP
 .B PORTAGE_LOG_FILTER_FILE_CMD
 This variable specifies a command that filters build log output to a
 log file. In order to filter ANSI escape codes from build logs,