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From: John Garry <john.garry@huawei.com>
To: Ming Lei <ming.lei@redhat.com>
Cc: Robin Murphy <robin.murphy@arm.com>,
	<linux-kernel@vger.kernel.org>, <linux-nvme@lists.infradead.org>,
	<iommu@lists.linux-foundation.org>,
	"Will Deacon" <will@kernel.org>,
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node
Date: Wed, 28 Jul 2021 11:38:18 +0100	[thread overview]
Message-ID: <ead87bf2-ddfa-eb67-db44-9619c6cdb714@huawei.com> (raw)
In-Reply-To: <CAFj5m9J+9vO=CK3uPP+va5EoWffZj9ruSRe2fDDLXn+AE971CQ@mail.gmail.com>

On 28/07/2021 02:32, Ming Lei wrote:
> On Mon, Jul 26, 2021 at 3:51 PM John Garry<john.garry@huawei.com>  wrote:
>> On 23/07/2021 11:21, Ming Lei wrote:
>>>> Thanks, I was also going to suggest the latter, since it's what
>>>> arm_smmu_cmdq_issue_cmdlist() does with IRQs masked that should be most
>>>> indicative of where the slowness most likely stems from.
>>> The improvement from 'iommu.strict=0' is very small:
>>>
>> Have you tried turning off the IOMMU to ensure that this is really just
>> an IOMMU problem?
>>
>> You can try setting CONFIG_ARM_SMMU_V3=n in the defconfig or passing
>> cmdline param iommu.passthrough=1 to bypass the the SMMU (equivalent to
>> disabling for kernel drivers).
> Bypassing SMMU via iommu.passthrough=1 basically doesn't make a difference
> on this issue.

A ~90% throughput drop still seems to me to be too high to be a software 
issue. More so since I don't see similar on my system. And that 
throughput drop does not lead to a total CPU usage drop, from the fio log.

Do you know if anyone has run memory benchmark tests on this board to 
find out NUMA effect? I think lmbench or stream could be used for this.

Testing network performance in an equivalent fashion to storage could 
also be an idea.

Thanks,
John

> 
> And from fio log, submission latency is good, but completion latency
> is pretty bad,
> and maybe it is something that writing to PCI memory isn't committed to HW in
> time?


  reply	other threads:[~2021-07-28 10:38 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-09  8:38 [bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node Ming Lei
2021-07-09 10:16 ` Russell King (Oracle)
2021-07-09 14:21   ` Ming Lei
2021-07-09 10:26 ` Robin Murphy
2021-07-09 11:04   ` John Garry
2021-07-09 12:34     ` Robin Murphy
2021-07-09 14:24   ` Ming Lei
2021-07-19 16:14     ` John Garry
2021-07-21  1:40       ` Ming Lei
2021-07-21  9:23         ` John Garry
2021-07-21  9:59           ` Ming Lei
2021-07-21 11:07             ` John Garry
2021-07-21 11:58               ` Ming Lei
2021-07-22  7:58               ` Ming Lei
2021-07-22 10:05                 ` John Garry
2021-07-22 10:19                   ` Ming Lei
2021-07-22 11:12                     ` John Garry
2021-07-22 12:53                       ` Marc Zyngier
2021-07-22 13:54                         ` John Garry
2021-07-22 15:54                       ` Ming Lei
2021-07-22 17:40                         ` Robin Murphy
2021-07-23 10:21                           ` Ming Lei
2021-07-26  7:51                             ` John Garry
2021-07-28  1:32                               ` Ming Lei
2021-07-28 10:38                                 ` John Garry [this message]
2021-07-28 15:17                                   ` Ming Lei
2021-07-28 15:39                                     ` Robin Murphy
2021-08-10  9:36                                     ` John Garry
2021-08-10 10:35                                       ` Ming Lei
2021-07-27 17:08                             ` Robin Murphy

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