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authorEmilio G. Cota <cota@braap.org>2017-08-08 13:53:15 -0400
committerPaolo Bonzini <pbonzini@redhat.com>2018-08-23 18:46:25 +0200
commitfe9959a275fc7b4744e49201a390627b3adda597 (patch)
treeb6d4d8e7b58866e9fa1ffd3a76ec1a1581065cc0 /net/colo.h
parentc04649eeeaf5f84ba9e43d0c4ffbe1719b0d940c (diff)
qsp: QEMU's Synchronization Profiler
The goal of this module is to profile synchronization primitives (i.e. mutexes, recursive mutexes and condition variables) so that scalability issues can be quickly diagnosed. Sync primitives are profiled by QSP based on the vaddr of the object accessed as well as the call site (file:line_nr). That means the same object called from two different call sites will be tracked in separate entries, which might be reported together or separately (see subsequent commit on call site coalescing). Some perf numbers: Host: Intel(R) Core(TM) i7-6700K CPU @ 4.00GHz Command: taskset -c 0 tests/atomic_add-bench -d 5 -m - Before: 54.80 Mops/s - After: 54.75 Mops/s That is, a negligible slowdown due to the now indirect call to qemu_mutex_lock. Note that using a branch instead of an indirect call introduces a more severe slowdown (53.65 Mops/s, i.e. 2% slowdown). Enabling the profiler (with -p, added in this series) is more interesting: - No profiling: 54.75 Mops/s - W/ profiling: 12.53 Mops/s That is, a 4.36X slowdown. We can break down this slowdown by removing the get_clock calls or the entry lookup: - No profiling: 54.75 Mops/s - W/o get_clock: 25.37 Mops/s - W/o entry lookup: 19.30 Mops/s - W/ profiling: 12.53 Mops/s Signed-off-by: Emilio G. Cota <cota@braap.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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