From: Sudeep Holla <sudeep.holla@arm.com>
To: Vikram Mulukutla <markivx@codeaurora.org>
Cc: Sudeep Holla <sudeep.holla@arm.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will.deacon@arm.com>,
linux-kernel@vger.kernel.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel-owner@vger.kernel.org
Subject: Re: spin_lock behavior with ARM64 big.Little/HMP
Date: Mon, 21 Nov 2016 15:21:36 +0000 [thread overview]
Message-ID: <f17207e7-e58c-2e42-04a8-50ed83a9616f@arm.com> (raw)
In-Reply-To: <f9fc9549d801fece7422d97d5d89df8b@codeaurora.org>
On 18/11/16 20:22, Vikram Mulukutla wrote:
>
> Hi Sudeep,
>
> Thanks for taking a look!
>
> On 2016-11-18 02:30, Sudeep Holla wrote:
>> Hi Vikram,
>>
>> On 18/11/16 02:22, Vikram Mulukutla wrote:
>>> Hello,
>>>
>>> This isn't really a bug report, but just a description of a
>>> frequency/IPC
>>> dependent behavior that I'm curious if we should worry about. The
>>> behavior
>>> is exposed by questionable design so I'm leaning towards don't-care.
>>>
>>> Consider these threads running in parallel on two ARM64 CPUs running
>>> mainline
>>> Linux:
>>>
>>
>> Are you seeing this behavior with the mainline kernel on any platforms
>> as we have a sort of workaround for this ?
>>
>
> If I understand that workaround correctly, the ARM timer event stream is
> used
> to periodically wake up CPUs that are waiting in WFE, is that right? I
> think
> my scenario below may be different because LittleCPU doesn't actually wait
> on a WFE event in the loop that is trying to increment lock->next, i.e.
> it's
> stuck in the following loop:
>
> ARM64_LSE_ATOMIC_INSN(
> /* LL/SC */
> " prfm pstl1strm, %3\n"
> "1: ldaxr %w0, %3\n"
> " add %w1, %w0, %w5\n"
> " stxr %w2, %w1, %3\n"
> " cbnz %w2, 1b\n",
>
Interesting. Just curious if this is r0p0/p1 A53 ? If so, is the errata
819472 enabled ?
--
Regards,
Sudeep
next prev parent reply other threads:[~2016-11-21 15:21 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-18 2:22 Vikram Mulukutla
2016-11-18 10:30 ` Sudeep Holla
2016-11-18 20:22 ` Vikram Mulukutla
2016-11-21 15:21 ` Sudeep Holla [this message]
2017-03-30 4:12 ` Vikram Mulukutla
2017-03-30 10:23 ` Sudeep Holla
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