From: Adrian Hunter <adrian.hunter@intel.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Leo Yan <leo.yan@linaro.org>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Namhyung Kim <namhyung@kernel.org>,
Andi Kleen <ak@linux.intel.com>,
linux-perf-users@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1 2/2] perf auxtrace: Optimize barriers with load-acquire and store-release
Date: Tue, 1 Jun 2021 12:45:16 +0300 [thread overview]
Message-ID: <4af1a96d-e03c-f1b4-ebce-ca869318c8cf@intel.com> (raw)
In-Reply-To: <YLX7OhK37QmfeOwu@hirez.programming.kicks-ass.net>
On 1/06/21 12:17 pm, Peter Zijlstra wrote:
> On Tue, Jun 01, 2021 at 12:07:31PM +0300, Adrian Hunter wrote:
>> __sync_xxx_compare_and_swap is out-of-date now. This page:
>>
>> https://gcc.gnu.org/onlinedocs/gcc/_005f_005fsync-Builtins.html#g_t_005f_005fsync-Builtins
>>
>> recommends '__atomic' builtins instead.
>
> perf doesn't seem to use that.
I guess we could drop support for the compat case; add validation:
"Error, 32-bit perf cannot record AUX area traces from a 64-bit kernel.
Please use a 64-bit version of perf instead."
>
>> Since atomics are needed only for the "compat" case (i.e. 32-bit perf with 64-bit kernel)
>> you could try to find an elegant way to check for a 64-bit kernel, and avoid the atomics
>> for a 32-bit perf with 32-bit kernel.
>
> Most 32bit archs cannot do 64bit atomics. I suppose the only reason this
> doesn't explode is because the aux stuff isn't supported on many
> architectures?
>
Yes but presumably the race itself is unlikely since the upper byte changes only once every 4GiB.
next prev parent reply other threads:[~2021-06-01 9:45 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-19 14:03 [PATCH v1 1/2] perf auxtrace: Change to use SMP memory barriers Leo Yan
2021-05-19 14:03 ` [PATCH v1 2/2] perf auxtrace: Optimize barriers with load-acquire and store-release Leo Yan
2021-05-31 15:10 ` Leo Yan
2021-05-31 15:55 ` Peter Zijlstra
2021-05-31 19:03 ` Adrian Hunter
2021-06-01 6:33 ` Leo Yan
2021-06-01 6:58 ` Peter Zijlstra
2021-06-01 9:07 ` Adrian Hunter
2021-06-01 9:17 ` Peter Zijlstra
2021-06-01 9:45 ` Adrian Hunter [this message]
2021-06-01 9:48 ` Peter Zijlstra
2021-06-01 14:56 ` Leo Yan
2021-06-01 6:48 ` Peter Zijlstra
2021-05-27 7:54 ` [PATCH v1 1/2] perf auxtrace: Change to use SMP memory barriers Adrian Hunter
2021-05-27 8:11 ` Peter Zijlstra
2021-05-27 8:25 ` Adrian Hunter
2021-05-27 9:24 ` Adrian Hunter
2021-05-27 9:57 ` Peter Zijlstra
2021-05-31 14:53 ` Leo Yan
2021-05-31 15:48 ` Peter Zijlstra
2021-06-01 3:21 ` Leo Yan
2021-05-27 9:45 ` Peter Zijlstra
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