From: Arnaldo Carvalho de Melo <acme@kernel.org>
To: Leo Yan <leo.yan@linaro.org>
Cc: peterz@infradead.org, Mark Rutland <mark.rutland@arm.com>,
Ingo Molnar <mingo@redhat.com>, Wei Li <liwei391@huawei.com>,
Al Grant <al.grant@arm.com>,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
"Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>,
Nick Desaulniers <ndesaulniers@google.com>,
Kemeng Shi <shikemeng@huawei.com>,
Ian Rogers <irogers@google.com>,
John Garry <john.garry@huawei.com>,
Stephane Eranian <eranian@google.com>,
Nick Gasson <nick.gasson@arm.com>,
Andi Kleen <ak@linux.intel.com>,
Steve MacLean <Steve.MacLean@microsoft.com>,
"Gustavo A. R. Silva" <gustavoars@kernel.org>,
Kan Liang <kan.liang@linux.intel.com>,
Will Deacon <will@kernel.org>, James Clark <james.clark@arm.com>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3 2/6] perf tsc: Add rdtsc() for Arm64
Date: Fri, 4 Sep 2020 16:08:26 -0300 [thread overview]
Message-ID: <20200904190826.GC3753976@kernel.org> (raw)
In-Reply-To: <20200903022354.GA1583@leoy-ThinkPad-X240s>
Em Thu, Sep 03, 2020 at 10:23:54AM +0800, Leo Yan escreveu:
> Hi Peter,
>
> On Wed, Sep 02, 2020 at 03:48:05PM +0200, Peter Zijlstra wrote:
> > On Wed, Sep 02, 2020 at 02:21:27PM +0100, Leo Yan wrote:
> > > The system register CNTVCT_EL0 can be used to retrieve the counter from
> > > user space. Add rdtsc() for Arm64.
> >
> > > +u64 rdtsc(void)
> > > +{
> > > + u64 val;
> >
> > Would it make sense to put a comment in that this counter is/could-be
> > 'short' ? Because unlike x86-TSC, this thing isn't architecturally
> > specified to be 64bits wide.
>
> Will add below comments:
>
> According to ARM DDI 0487F.c, from Armv8.0 to Armv8.5 inclusive, the
> system counter is at least 56 bits wide; from Armv8.6, the counter must
> be 64 bits wide. So the system counter could be less than 64 bits wide
> and it is attributed with the flag 'cap_user_time_short' is true.
Ok, so waiting for v4.
- Arnaldo
next prev parent reply other threads:[~2020-09-04 19:08 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-02 13:21 [PATCH v3 0/6] Perf tool: Support TSC for Arm64 Leo Yan
2020-09-02 13:21 ` [PATCH v3 1/6] perf tsc: Move out common functions from x86 Leo Yan
2020-09-02 13:21 ` [PATCH v3 2/6] perf tsc: Add rdtsc() for Arm64 Leo Yan
2020-09-02 13:48 ` peterz
2020-09-03 2:23 ` Leo Yan
2020-09-04 19:08 ` Arnaldo Carvalho de Melo [this message]
2020-09-02 13:21 ` [PATCH v3 3/6] perf tsc: Calculate timestamp with cap_user_time_short Leo Yan
2020-09-02 13:21 ` [PATCH v3 4/6] perf tsc: Support cap_user_time_short for event TIME_CONV Leo Yan
2020-09-02 13:21 ` [PATCH v3 5/6] perf tests tsc: Make tsc testing as a common testing Leo Yan
2020-09-02 13:21 ` [PATCH v3 6/6] perf tests tsc: Add checking helper is_supported() Leo Yan
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