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From: Rob Herring <robh@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jonathan Corbet <corbet@lwn.net>,
	Catalin Marinas <catalin.marinas@arm.com>,
	Ingo Molnar <mingo@redhat.com>,
	Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	x86@kernel.org, "H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-perf-users@vger.kernel.org
Subject: Re: [PATCH v12 2/5] perf: Add a counter for number of user access events in context
Date: Fri, 3 Dec 2021 09:58:15 -0600	[thread overview]
Message-ID: <CAL_JsqJ9kkch_SB6LT_fwxk9QS36zbwsj5wu+dtY7yWe6SEMug@mail.gmail.com> (raw)
In-Reply-To: <87zgpl9rqq.ffs@tglx>

On Tue, Nov 30, 2021 at 4:57 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Wed, Oct 27 2021 at 15:16, Rob Herring wrote:
> > For controlling user space counter access, we need to know if any event
> > in a context (currently scheduled or not) is using user space counters.
>
> Who is 'we'?
>
> Come on. How is someone without context supposed to figure out that 'we'
> means ARM64 when staring at that changelog a year later?
>
> Is it really that hard to write coherent changelogs which make sense on
> their own and actually follow Documentation/process/ which exists for a
> reason?

I've rewritten it like this:

On arm64, user space counter access will be controlled differently
compared to x86. On x86, access in the strictest mode is enabled for all
tasks in an MM when any event is mmap'ed. For arm64, access is
explicitly requested for an event and only enabled when the event's
context is active. This avoids hooks into the arch context switch code
and gives better control of when access is enabled.

In order to configure user space access when the PMU is enabled, it is
necessary to know if any event (currently active or not) in the current
context has user space accessed enabled. Add a counter similar to other
counters in the context to avoid walking the event list every time.

WARNING: multiple messages have this Message-ID (diff)
From: Rob Herring <robh@kernel.org>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: Will Deacon <will@kernel.org>,
	Mark Rutland <mark.rutland@arm.com>,
	 Peter Zijlstra <peterz@infradead.org>,
	Jonathan Corbet <corbet@lwn.net>,
	 Catalin Marinas <catalin.marinas@arm.com>,
	Ingo Molnar <mingo@redhat.com>,
	 Arnaldo Carvalho de Melo <acme@kernel.org>,
	Alexander Shishkin <alexander.shishkin@linux.intel.com>,
	 Jiri Olsa <jolsa@redhat.com>, Namhyung Kim <namhyung@kernel.org>,
	Borislav Petkov <bp@alien8.de>,
	x86@kernel.org,  "H. Peter Anvin" <hpa@zytor.com>,
	linux-kernel@vger.kernel.org,
	 linux-arm-kernel@lists.infradead.org,
	linux-perf-users@vger.kernel.org
Subject: Re: [PATCH v12 2/5] perf: Add a counter for number of user access events in context
Date: Fri, 3 Dec 2021 09:58:15 -0600	[thread overview]
Message-ID: <CAL_JsqJ9kkch_SB6LT_fwxk9QS36zbwsj5wu+dtY7yWe6SEMug@mail.gmail.com> (raw)
In-Reply-To: <87zgpl9rqq.ffs@tglx>

On Tue, Nov 30, 2021 at 4:57 PM Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Wed, Oct 27 2021 at 15:16, Rob Herring wrote:
> > For controlling user space counter access, we need to know if any event
> > in a context (currently scheduled or not) is using user space counters.
>
> Who is 'we'?
>
> Come on. How is someone without context supposed to figure out that 'we'
> means ARM64 when staring at that changelog a year later?
>
> Is it really that hard to write coherent changelogs which make sense on
> their own and actually follow Documentation/process/ which exists for a
> reason?

I've rewritten it like this:

On arm64, user space counter access will be controlled differently
compared to x86. On x86, access in the strictest mode is enabled for all
tasks in an MM when any event is mmap'ed. For arm64, access is
explicitly requested for an event and only enabled when the event's
context is active. This avoids hooks into the arch context switch code
and gives better control of when access is enabled.

In order to configure user space access when the PMU is enabled, it is
necessary to know if any event (currently active or not) in the current
context has user space accessed enabled. Add a counter similar to other
counters in the context to avoid walking the event list every time.

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-12-03 15:58 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-10-27 20:16 [PATCH v12 0/5] Another version of arm64 userspace counter access support Rob Herring
2021-10-27 20:16 ` Rob Herring
2021-10-27 20:16 ` [PATCH v12 1/5] x86: perf: Move RDPMC event flag to a common definition Rob Herring
2021-10-27 20:16   ` Rob Herring
2021-11-30 22:51   ` Thomas Gleixner
2021-11-30 22:51     ` Thomas Gleixner
2021-10-27 20:16 ` [PATCH v12 2/5] perf: Add a counter for number of user access events in context Rob Herring
2021-10-27 20:16   ` Rob Herring
2021-11-30 22:57   ` Thomas Gleixner
2021-11-30 22:57     ` Thomas Gleixner
2021-12-03 15:58     ` Rob Herring [this message]
2021-12-03 15:58       ` Rob Herring
2021-12-04 14:23       ` Thomas Gleixner
2021-12-04 14:23         ` Thomas Gleixner
2021-10-27 20:16 ` [PATCH v12 3/5] arm64: perf: Add userspace counter access disable switch Rob Herring
2021-10-27 20:16   ` Rob Herring
2021-10-27 20:16 ` [PATCH v12 4/5] arm64: perf: Enable PMU counter userspace access for perf event Rob Herring
2021-10-27 20:16   ` Rob Herring
2021-10-27 20:16 ` [PATCH v12 5/5] Documentation: arm64: Document PMU counters access from userspace Rob Herring
2021-10-27 20:16   ` Rob Herring
2021-11-15 16:57 ` [PATCH v12 0/5] Another version of arm64 userspace counter access support Rob Herring
2021-11-15 16:57   ` Rob Herring
2021-11-30 21:56   ` Rob Herring
2021-11-30 21:56     ` Rob Herring

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