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SubjectRe: [tip:perf/core] perf/x86/intel: Force resched when TFA sysctl is modified
On Tue, Apr 16, 2019 at 12:28:00PM -0400, Vince Weaver wrote:
> On Tue, 16 Apr 2019, tip-bot for Stephane Eranian wrote:
>
> > Commit-ID: f447e4eb3ad1e60d173ca997fcb2ef2a66f12574
> > Gitweb: https://git.kernel.org/tip/f447e4eb3ad1e60d173ca997fcb2ef2a66f12574
> > Author: Stephane Eranian <eranian@google.com>
> > AuthorDate: Mon, 8 Apr 2019 10:32:52 -0700
> > Committer: Ingo Molnar <mingo@kernel.org>
> > CommitDate: Tue, 16 Apr 2019 12:19:35 +0200
> >
> > perf/x86/intel: Force resched when TFA sysctl is modified
>
> What's TFA? Tuna-fish-alarm? Nowhere in the commit or in the code does
> it ever say what a TFA is or why we'd want to resched when it is modified.

See commit: 400816f60c54 ("perf/x86/intel: Implement support for TSX Force Abort")

Author: Peter Zijlstra (Intel) <peterz@infradead.org>
Date: Tue Mar 5 22:23:18 2019 +0100

perf/x86/intel: Implement support for TSX Force Abort

Skylake (and later) will receive a microcode update to address a TSX
errata. This microcode will, on execution of a TSX instruction
(speculative or not) use (clobber) PMC3. This update will also provide
a new MSR to change this behaviour along with a CPUID bit to enumerate
the presence of this new MSR.

When the MSR gets set; the microcode will no longer use PMC3 but will
Force Abort every TSX transaction (upon executing COMMIT).

When TSX Force Abort (TFA) is allowed (default); the MSR gets set when
PMC3 gets scheduled and cleared when, after scheduling, PMC3 is
unused.

When TFA is not allowed; clear PMC3 from all constraints such that it
will not get used.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

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