From: Leo Yan <leo.yan@linaro.org>
To: James Clark <james.clark@arm.com>
Cc: linux-kernel@vger.kernel.org, linux-perf-users@vger.kernel.org,
broonie@kernel.org, acme@kernel.org, german.gomez@arm.com,
mathieu.poirier@linaro.org, john.garry@huawei.com,
Will Deacon <will@kernel.org>, Mike Leach <mike.leach@linaro.org>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@kernel.org>, Namhyung Kim <namhyung@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v2 4/4] perf tools: arm64: Add support for VG register
Date: Wed, 18 May 2022 17:57:35 +0800 [thread overview]
Message-ID: <20220518095735.GB430350@leoy-ThinkPad-X240s> (raw)
In-Reply-To: <ca02e8f5-04bd-01ff-7b57-0fd08a1e2359@arm.com>
On Wed, May 18, 2022 at 10:44:57AM +0100, James Clark wrote:
[...]
> >> + if (getauxval(AT_HWCAP) & HWCAP_SVE)
> >> + attr.sample_regs_user |= SMPL_REG_MASK(PERF_REG_ARM64_VG);
> >> +
> >> + /*
> >> + * Check if the pmu supports perf extended regs, before
> >> + * returning the register mask to sample.
> >> + */
> >> + if (attr.sample_regs_user != PERF_REGS_MASK) {
> >> + event_attr_init(&attr);
> >> + fd = sys_perf_event_open(&attr, 0, -1, -1, 0);
> >> + if (fd != -1) {
> >> + close(fd);
> >> + return attr.sample_regs_user;
> >> + }
> >> + }
> >
> > Just curious, since we can know SVE is supported from reading
> > auxiliary value, can we directly return the register mask as below?
> >
> > PERF_REGS_MASK | SMPL_REG_MASK(PERF_REG_ARM64_VG);
>
> I was trying to cover the case where the system supports SVE, but
> the kernel doesn't have my changes to add the VG register yet.
>
> Technically I could just attempt to open the event without checking
> for SVE first and see if it works or not. But I preferred to be
> explicit so it's obvious why we're doing that.
Understand; LGTM.
Reviewed-by: Leo Yan <leo.yan@linaro.org>
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next prev parent reply other threads:[~2022-05-18 9:58 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-17 10:20 [PATCH v2 0/2] perf: arm64: Tools support for Dwarf unwinding through SVE functions James Clark
2022-05-17 10:20 ` [PATCH v2 1/4] perf tools: arm64: Copy perf_regs.h from the kernel James Clark
2022-05-17 10:50 ` Leo Yan
2022-05-17 10:20 ` [PATCH v2 2/4] perf tools: Use dynamic register set for Dwarf unwind James Clark
2022-05-17 11:03 ` Leo Yan
2022-05-18 13:25 ` James Clark
2022-05-18 14:00 ` Leo Yan
2022-05-17 10:20 ` [PATCH v2 3/4] perf tools: arm64: Decouple Libunwind register names from Perf James Clark
2022-05-17 12:54 ` Leo Yan
2022-05-17 10:20 ` [PATCH v2 4/4] perf tools: arm64: Add support for VG register James Clark
2022-05-17 13:19 ` Leo Yan
2022-05-18 9:44 ` James Clark
2022-05-18 9:57 ` Leo Yan [this message]
2022-05-17 14:58 ` [PATCH v2 0/2] perf: arm64: Tools support for Dwarf unwinding through SVE functions Arnaldo Carvalho de Melo
2022-05-20 11:46 ` German Gomez
2022-05-20 12:32 ` Arnaldo Carvalho de Melo
2022-05-20 14:52 ` James Clark
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