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author | Frederic Weisbecker <frederic@kernel.org> | 2019-10-03 19:17:45 +0300 |
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committer | Ingo Molnar <mingo@kernel.org> | 2019-10-09 13:39:26 +0300 |
commit | 8d495477d62e4397207f22a432fcaa86d9f2bc2d (patch) | |
tree | ce4a558f94f134db1ad239bf4c4b2556c578923d /kernel/sched/topology.c | |
parent | f83eeb1a01689b2691f6f56629ac9f66de8d41c2 (diff) | |
download | linux-8d495477d62e4397207f22a432fcaa86d9f2bc2d.tar.xz |
sched/cputime: Spare a seqcount lock/unlock cycle on context switch
On context switch we are locking the vtime seqcount of the scheduling-out
task twice:
* On vtime_task_switch_common(), when we flush the pending vtime through
vtime_account_system()
* On arch_vtime_task_switch() to reset the vtime state.
This is pointless as these actions can be performed without the need
to unlock/lock in the middle. The reason these steps are separated is to
consolidate a very small amount of common code between
CONFIG_VIRT_CPU_ACCOUNTING_GEN and CONFIG_VIRT_CPU_ACCOUNTING_NATIVE.
Performance in this fast path is definitely a priority over artificial
code factorization so split the task switch code between GEN and
NATIVE and mutualize the parts than can run under a single seqcount
locked block.
As a side effect, vtime_account_idle() becomes included in the seqcount
protection. This happens to be a welcome preparation in order to
properly support kcpustat under vtime in the future and fetch
CPUTIME_IDLE without race.
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Link: https://lkml.kernel.org/r/20191003161745.28464-3-frederic@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/sched/topology.c')
0 files changed, 0 insertions, 0 deletions