From: Frederic Weisbecker <fweisbec@gmail.com>
To: Kevin Hilman <khilman@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Li Zhong <zhong@linux.vnet.ibm.com>,
Namhyung Kim <namhyung.kim@lge.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Paul Gortmaker <paul.gortmaker@windriver.com>,
Peter Zijlstra <peterz@infradead.org>,
Steven Rostedt <rostedt@goodmis.org>,
Thomas Gleixner <tglx@linutronix.de>,
Sedat Dilek <sedat.dilek@gmail.com>,
Gleb Natapov <gleb@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Tony Luck <tony.luck@intel.com>,
Fenghua Yu <fenghua.yu@intel.com>
Subject: Re: [GIT PULL] cputime: Full dynticks task/cputime accounting v7
Date: Wed, 20 Feb 2013 16:44:24 +0100 [thread overview]
Message-ID: <CAFTL4hzH7avJLAvjBf3Px44s-BRRezTekrdQR4vSUhyFTYXwHA@mail.gmail.com> (raw)
In-Reply-To: <87k3qa7333.fsf@linaro.org>
2013/2/15 Kevin Hilman <khilman@linaro.org>:
> Frederic Weisbecker <fweisbec@gmail.com> writes:
>
>> Ingo,
>>
>> Please pull the new full dynticks cputime accounting code that
>> can be found at:
>>
>> git://git.kernel.org/pub/scm/linux/kernel/git/frederic/linux-dynticks.git
>> tags/full-dynticks-cputime-for-mingo
>>
>> My last concern is the dependency on CONFIG_64BIT. We rely on cputime_t
>> being u64 for reasonable nanosec granularity implementation. And therefore
>> we need a single instruction fetch to read kernel cpustat for atomicity
>> requirement against concurrent incrementation, which only 64 bit archs
>> can provide.
>
> Actually, moderately recent 32-bit ARMs can do atomic 64-bit load/stores
> too.
Does gcc automatically handle 64 bit store/loads in one way or does
that require specific CPU instructions?
>
> Also, is it just kernel_cpustat increments that need protection? or do
> the various reads of the task_struct's cputime fields also need
> protection (hmm, thinking twice, maybe those are already sufficiently
> protected by the vtime_seqlock?)
At least the task stats are protected with vtime_seqlock (hopefully I
haven't missed some). But per cpu or global stats are not.
>
>> It's probably no big deal to solve this issue. What we need is simply some
>> atomic accessors.
>
> What about using the atomic64_* accessors? Those would just use the
> native loads/stores on arches that have them, otherwise
> CONFIG_GENERIC_ATOMIC64 provides some fallbacks.
Yeah may be we can try this.
>
> To give it a try, below is a quick patch to convert kernel_cpustat to
> atomic64. I only got as far as compile testing and basic boot testing
> on a 32-bit ARM platform, but let me know if this is the right
> direction.
Ok, I'll comment on your second version.
>
>> There is just no emergency though as this new option depends on the context
>> tracking subsystem that only x86-64 (and soon ppc64) implements yet. And
>> this set is complex enough already. I think we can deal with that later.
>
> I've started working on the ARM version of the context_tracker, so
> "later" is coming quickly and I will do what I can to help this along.
Ok. Thanks.
next prev parent reply other threads:[~2013-02-20 15:44 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-01-28 19:03 [GIT PULL] cputime: Full dynticks task/cputime accounting v7 Frederic Weisbecker
2013-01-28 19:03 ` [PATCH 1/8] context_tracking: Export context state for generic vtime Frederic Weisbecker
2013-01-28 19:03 ` [PATCH 2/8] cputime: Librarize per nsecs resolution cputime definitions Frederic Weisbecker
2013-02-14 19:49 ` Kevin Hilman
2013-02-20 16:07 ` Frederic Weisbecker
2013-01-28 19:04 ` [PATCH 3/8] cputime: Move default nsecs_to_cputime() to jiffies based cputime file Frederic Weisbecker
2013-01-28 19:04 ` [PATCH 4/8] cputime: Generic on-demand virtual cputime accounting Frederic Weisbecker
2013-02-08 3:07 ` Stephen Rothwell
2013-02-08 3:14 ` Stephen Rothwell
2013-02-08 3:19 ` [PATCH] cputime: restore CPU_ACCOUNTING config defaults for PPC64 Stephen Rothwell
2013-02-08 15:18 ` [tip:sched/core] cputime: Restore " tip-bot for Stephen Rothwell
2013-02-08 14:31 ` [PATCH 4/8] cputime: Generic on-demand virtual cputime accounting Frederic Weisbecker
2013-01-28 19:04 ` [PATCH 5/8] cputime: Allow dynamic switch between tick/virtual based " Frederic Weisbecker
2013-01-28 19:04 ` [PATCH 6/8] cputime: Use accessors to read task cputime stats Frederic Weisbecker
2013-01-28 19:04 ` [PATCH 7/8] kvm: Prepare to add generic guest entry/exit callbacks Frederic Weisbecker
2013-01-28 19:04 ` [PATCH 8/8] cputime: Safely read cputime of full dynticks CPUs Frederic Weisbecker
2013-01-28 21:51 ` Sedat Dilek
2013-01-30 21:57 ` Sedat Dilek
2013-01-31 0:38 ` Frederic Weisbecker
2013-01-31 7:24 ` Sedat Dilek
2013-01-31 10:12 ` Frederic Weisbecker
2013-01-31 10:30 ` Sedat Dilek
2013-01-31 16:29 ` Frederic Weisbecker
2013-01-28 19:18 ` [GIT PULL] cputime: Full dynticks task/cputime accounting v7 Christoph Lameter
2013-01-28 19:21 ` Frederic Weisbecker
2013-01-28 20:14 ` Christoph Lameter
2013-01-29 1:42 ` Frederic Weisbecker
2013-01-29 0:02 ` Steven Rostedt
2013-01-29 1:36 ` Frederic Weisbecker
2013-01-29 2:36 ` Steven Rostedt
2013-01-29 2:39 ` Frederic Weisbecker
2013-01-29 2:44 ` Steven Rostedt
2013-01-29 3:29 ` Frederic Weisbecker
2013-01-29 4:38 ` Steven Rostedt
2013-01-29 15:12 ` Frederic Weisbecker
2013-01-29 16:46 ` Steven Rostedt
2013-01-29 16:55 ` Frederic Weisbecker
2013-01-29 17:08 ` Steven Rostedt
2013-01-29 21:26 ` Steven Rostedt
2013-01-29 21:37 ` Frederic Weisbecker
2013-02-15 1:55 ` Kevin Hilman
2013-02-15 14:04 ` Mats Liljegren
2013-02-15 15:06 ` Kevin Hilman
2013-02-20 15:53 ` Frederic Weisbecker
2013-02-20 17:53 ` Kevin Hilman
2013-02-20 15:44 ` Frederic Weisbecker [this message]
2013-02-20 18:48 ` Kevin Hilman
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