From: thunder.leizhen@huawei•com (Leizhen (ThunderTown))
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed in queue_inc_prod
Date: Mon, 26 Jun 2017 21:41:47 +0800 [thread overview]
Message-ID: <59510F1B.60304@huawei.com> (raw)
In-Reply-To: <59510C20.6000300@huawei.com>
On 2017/6/26 21:29, Leizhen (ThunderTown) wrote:
>
>
> On 2017/6/21 17:08, Will Deacon wrote:
>> On Wed, Jun 21, 2017 at 09:28:23AM +0800, Leizhen (ThunderTown) wrote:
>>> On 2017/6/20 19:35, Robin Murphy wrote:
>>>> On 20/06/17 12:04, Zhen Lei wrote:
>>>>> This function is protected by spinlock, and the latter will do memory
>>>>> barrier implicitly. So that we can safely use writel_relaxed. In fact, the
>>>>> dmb operation will lengthen the time protected by lock, which indirectly
>>>>> increase the locking confliction in the stress scene.
>>>>
>>>> If you remove the DSB between writing the commands (to Normal memory)
>>>> and writing the pointer (to Device memory), how can you guarantee that
>>>> the complete command is visible to the SMMU and it isn't going to try to
>>>> consume stale memory contents? The spinlock is irrelevant since it's
>>>> taken *before* the command is written.
>>> OK, I see, thanks. Let's me see if there are any other methods. And I think
>>> that this may should be done well by hardware.
>>
>> FWIW, I did use the _relaxed variants wherever I could when I wrote the
>> driver. There might, of course, be bugs, but it's not like the normal case
>> for drivers where the author didn't consider the _relaxed accessors
>> initially.
> A good news. I got a new idea and I will post v2 later.
[PATCH 0/5] arm-smmu: performance optimization
[PATCH 1/5] iommu/arm-smmu-v3: put off the execution of TLBI* to reduce lock confliction
I just sent.
>
>>
>> Will
>>
>> .
>>
>
--
Thanks!
BestRegards
prev parent reply other threads:[~2017-06-26 13:41 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-06-20 11:04 [PATCH 1/1] iommu/arm-smmu-v3: replace writel with writel_relaxed in queue_inc_prod Zhen Lei
2017-06-20 11:35 ` Robin Murphy
2017-06-21 1:28 ` Leizhen (ThunderTown)
2017-06-21 9:08 ` Will Deacon
2017-06-26 13:29 ` Leizhen (ThunderTown)
2017-06-26 13:41 ` Leizhen (ThunderTown) [this message]
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