From: Tim Chen <tim.c.chen@linux.intel.com>
To: Dave Hansen <dave.hansen@intel.com>,
Aubrey Li <aubrey.li@intel.com>,
tglx@linutronix.de, mingo@redhat.com, peterz@infradead.org,
hpa@zytor.com
Cc: ak@linux.intel.com, arjan@linux.intel.com,
linux-kernel@vger.kernel.org,
Aubrey Li <aubrey.li@linux.intel.com>
Subject: Re: [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks
Date: Tue, 11 Dec 2018 09:52:43 -0800 [thread overview]
Message-ID: <86ba7095-b877-cea6-3c07-8db2ff7fe02f@linux.intel.com> (raw)
In-Reply-To: <df1a1b5b-3e8b-5d96-12df-25be30c391af@intel.com>
On 12/11/18 9:18 AM, Dave Hansen wrote:
> On 12/10/18 4:24 PM, Aubrey Li wrote:
>> The tracking turns on the usage flag at the next context switch of
>> the task, but requires 3 consecutive context switches with no usage
>> to clear it. This decay is required because well-written AVX-512
>> applications are expected to clear this state when not actively using
>> AVX-512 registers.
>
> One concern about this: Given a HZ=1000 system, this means that the
> flag needs to get scanned every ~3ms. That's a pretty good amount of
> scanning on a system with hundreds or thousands of tasks running around.
>
> How many tasks does this scale to until you're eating up an entire CPU
> or two just scanning /proc?
>
The reason why I believe that an exponential decay average, or some
other kind of weighted decay of the AVX512 usage is better.
Tim
next prev parent reply other threads:[~2018-12-11 17:52 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-11 0:24 [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks Aubrey Li
2018-12-11 0:24 ` [PATCH v4 2/2] proc: add AVX-512 usage to /proc/pid/status Aubrey Li
2018-12-11 17:57 ` Tim Chen
2018-12-11 17:18 ` [PATCH v4 1/2] x86/fpu: track AVX-512 usage of tasks Dave Hansen
2018-12-11 17:52 ` Tim Chen [this message]
2018-12-11 17:53 ` Andi Kleen
2018-12-11 23:46 ` Li, Aubrey
2018-12-12 0:14 ` Arjan van de Ven
2018-12-12 0:59 ` Li, Aubrey
2018-12-12 1:06 ` Dave Hansen
2018-12-11 17:20 ` Dave Hansen
2018-12-12 0:34 ` Li, Aubrey
2018-12-12 0:39 ` Dave Hansen
2018-12-12 16:55 ` David Laight
2018-12-12 18:00 ` Andi Kleen
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