Mercurial > hg
view mercurial/compat.h @ 38732:be4984261611
merge: mark file gets as not thread safe (issue5933)
In default installs, this has the effect of disabling the thread-based
worker on Windows when manifesting files in the working directory. My
measurements have shown that with revlog-based repositories, Mercurial
spends a lot of CPU time in revlog code resolving file data. This ends
up incurring a lot of context switching across threads and slows down
`hg update` operations when going from an empty working directory to
the tip of the repo.
On mozilla-unified (246,351 files) on an i7-6700K (4+4 CPUs):
before: 487s wall
after: 360s wall (equivalent to worker.enabled=false)
cpus=2: 379s wall
Even with only 2 threads, the thread pool is still slower.
The introduction of the thread-based worker (02b36e860e0b) states that
it resulted in a "~50%" speedup for `hg sparse --enable-profile` and
`hg sparse --disable-profile`. This disagrees with my measurement
above. I theorize a few reasons for this:
1) Removal of files from the working directory is I/O - not CPU - bound
and should benefit from a thread pool (unless I/O is insanely fast
and the GIL release is near instantaneous). So tests like `hg sparse
--enable-profile` may exercise deletion throughput and aren't good
benchmarks for worker tasks that are CPU heavy.
2) The patch was authored by someone at Facebook. The results were
likely measured against a repository using remotefilelog. And I
believe that revision retrieval during working directory updates with
remotefilelog will often use a remote store, thus being I/O and not
CPU bound. This probably resulted in an overstated performance gain.
Since there appears to be a need to enable the thread-based worker with
some stores, I've made the flagging of file gets as thread safe
configurable. I've made it experimental because I don't want to formalize
a boolean flag for this option and because this attribute is best
captured against the store implementation. But we don't have a proper
store API for this yet. I'd rather cross this bridge later.
It is possible there are revlog-based repositories that do benefit from
a thread-based worker. I didn't do very comprehensive testing. If there
are, we may want to devise a more proper algorithm for whether to use
the thread-based worker, including possibly config options to limit the
number of threads to use. But until I see evidence that justifies
complexity, simplicity wins.
Differential Revision: https://phab.mercurial-scm.org/D3963
author | Gregory Szorc <gregory.szorc@gmail.com> |
---|---|
date | Wed, 18 Jul 2018 09:49:34 -0700 |
parents | f4433f2713d0 |
children | 11ed2eadf937 |
line wrap: on
line source
#ifndef _HG_COMPAT_H_ #define _HG_COMPAT_H_ #ifdef _WIN32 #ifdef _MSC_VER /* msvc 6.0 has problems */ #define inline __inline #if defined(_WIN64) typedef __int64 ssize_t; typedef unsigned __int64 uintptr_t; #else typedef int ssize_t; typedef unsigned int uintptr_t; #endif typedef signed char int8_t; typedef short int16_t; typedef long int32_t; typedef __int64 int64_t; typedef unsigned char uint8_t; typedef unsigned short uint16_t; typedef unsigned long uint32_t; typedef unsigned __int64 uint64_t; #else #include <stdint.h> #endif #else /* not windows */ #include <sys/types.h> #if defined __BEOS__ && !defined __HAIKU__ #include <ByteOrder.h> #else #include <arpa/inet.h> #endif #include <inttypes.h> #endif #if defined __hpux || defined __SUNPRO_C || defined _AIX #define inline #endif #ifdef __linux #define inline __inline #endif #endif