log/Log.cc: speed optimizations. Merged 3 writes into 1. #6307
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Got rid of std::string construction. More unification on syslog,stderr,fd. Signed-off-by: Adam Kupczyk <akupczyk@mirantis.com>
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| if (r < 0) | ||
| cerr << "problem writing to " << m_log_file << ": " << cpp_strerror(r) << std::endl; | ||
| } | ||
| buflen += e->snprintf(buf + buflen, sizeof(buf) - buflen - 1 ); |
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Good catch! I bet we can do even better with something that looks like pwritev(2)... then we avoid doing a memcpy into buf entirely, and instead construct an iovec array (there should be a max of 3 or 4 distinct inputs). The write or pwritev syscall is doing another copy anyway, so the one into buf shouldn't be necessary.
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I have tried using writev but it is actually slower.
Below using writev vs using memcpy to make 1 buffer.
size= 6 IOVS=3 time=107768usec
size= 6 WRITE time=84712usec
size= 12 IOVS=3 time=131376usec
size= 12 WRITE time=120907usec
size= 24 IOVS=3 time=183488usec
size= 24 WRITE time=172170usec
size= 48 IOVS=3 time=271790usec
size= 48 WRITE time=271460usec
size= 96 IOVS=3 time=674332usec
size= 96 WRITE time=424097usec
size=192 IOVS=3 time=769107usec
size=192 WRITE time=784972usec
size=384 IOVS=3 time=2253296usec
size=384 WRITE time=1509636usec
size=768 IOVS=3 time=2977487usec
size=768 WRITE time=2974786usec
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It make sense to me that very small vector will result in bad performance. I guess most of logs should be small enough
log/Log.cc: speed optimizations. Merged 3 writes into 1. Reviewed-by: Sage Weil <sage@redhat.com>
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Oops.. this passed testing but I merged too soon (and reverted). Two issues: 1- This is putting lot sof \0 in the log output. View a resulting log with 'less' to see. Thanks! |
Got rid of std::string construction.
More unification on syslog,stderr,fd.
Signed-off-by: Adam Kupczyk akupczyk@mirantis.com