From: Catalin Marinas <catalin.marinas@arm.com>
To: Leo Yan <leo.yan@linaro.org>
Cc: Kees Cook <keescook@chromium.org>, Will Deacon <will@kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Ard Biesheuvel <ardb@kernel.org>,
Sami Tolvanen <samitolvanen@google.com>,
Nicholas Piggin <npiggin@gmail.com>,
James Morse <james.morse@arm.com>, Marc Zyngier <maz@kernel.org>,
Joey Gouly <joey.gouly@arm.com>,
Peter Collingbourne <pcc@google.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
"Peter Zijlstra (Intel)" <peterz@infradead.org>,
Stephane Eranian <eranian@google.com>,
James Clark <james.clark@arm.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [RFCv1 4/4] perf: arm_spe: Dynamically switch PID tracing to contextidr
Date: Fri, 3 Dec 2021 16:22:42 +0000 [thread overview]
Message-ID: <YapEUlcyDZ6TuE6n@arm.com> (raw)
In-Reply-To: <20211101152835.GB375622@leoy-ThinkPad-X240s>
On Mon, Nov 01, 2021 at 11:28:35PM +0800, Leo Yan wrote:
> On Thu, Oct 21, 2021 at 08:49:46AM -0700, Kees Cook wrote:
> > On Thu, Oct 21, 2021 at 09:45:30PM +0800, Leo Yan wrote:
> > > Now Arm64 provides API for enabling and disable PID tracing, Arm SPE
> > > driver invokes these functions to dynamically enable it during
> > > profiling when the program runs in root PID name space, and disable PID
> > > tracing when the perf event is stopped.
> > >
> > > Device drivers should not depend on CONFIG_PID_IN_CONTEXTIDR for PID
> > > tracing, so this patch uses the consistent condition for setting bit
> > > EL1_CX for PMSCR.
> >
> > My own preference here would be to not bother with the new
> > enable/disable helpers, but just open code it right here. (Save a patch
> > and is the only user.) But I defer to the taste of arm64 maintainers. :)
>
> Before I send out a new version for this patch set (for support
> dynamic PID tracing on Arm64), I'd like to get your opinions for two
> things:
>
> - Firstly, as Kees suggested to directly use variable
> 'contextidr_in_use' in drivers, which is exported as GPL symbol,
> it's not necessarily to add two helpers contextidr_{enable|disable}().
> What's your preference for this?
My preference would be to keep the helpers.
> - Secondly, now this patch set only support dynamic PID tracing for
> Arm64; and there would be two customers to use dynamic PID tracing:
> Arm SPE and Coresight ETMv4.x. So this patch set doesn't support
> dynamic PID tracing for Arm32 (under arch/arm).
>
> Do you accept this patch set for enabling PID tracing on Arm64 and we
> can defer to support Arm32 when really need PID tracing on Arm32?
> Or we should enable PID dynamic tracing for Arm64 and Arm32 in one
> go?
If it doesn't break arm32, it's fine by me.
What's the cost of always enabling CONFIG_PID_IN_CONTEXTIDR? If it's
negligible, I'd not bother at all with any of the enabling/disabling.
Another question: can you run multiple instances of SPE for different
threads on different CPUs? What happens to the global contextidr_in_use
key when one of them stops?
--
Catalin
next prev parent reply other threads:[~2021-12-03 16:22 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-21 13:45 [RFCv1 0/4] arm64: Use static key for PID in CONTEXTIDR Leo Yan
2021-10-21 13:45 ` [RFCv1 1/4] arm64: Use static key for tracing " Leo Yan
2021-10-21 14:33 ` James Clark
2021-10-21 14:37 ` Leo Yan
2021-10-21 15:47 ` Kees Cook
2021-10-21 13:45 ` [RFCv1 2/4] arm64: entry: Always apply workaround for contextidr_el1 Leo Yan
2021-10-21 13:45 ` [RFCv1 3/4] arm64: Introduce functions for controlling PID tracing Leo Yan
2021-10-21 13:45 ` [RFCv1 4/4] perf: arm_spe: Dynamically switch PID tracing to contextidr Leo Yan
2021-10-21 15:49 ` Kees Cook
2021-10-22 2:09 ` Leo Yan
2021-11-01 15:28 ` Leo Yan
2021-12-03 16:22 ` Catalin Marinas [this message]
2021-12-05 13:51 ` Leo Yan
2021-12-07 11:48 ` Catalin Marinas
2021-12-07 12:31 ` Leo Yan
2021-12-08 17:29 ` Catalin Marinas
2021-12-10 7:59 ` Leo Yan
2021-12-17 7:58 ` Leo Yan
2022-01-17 18:48 ` Catalin Marinas
2022-02-01 13:02 ` Leo Yan
2021-10-22 15:36 ` James Clark
2021-10-22 15:40 ` James Clark
2021-10-22 16:23 ` James Clark
2021-10-24 10:25 ` Leo Yan
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