From: Cong Wang <xiyou.wangcong@gmail.com>
To: Robin Murphy <robin.murphy@arm.com>
Cc: iommu@lists.linux-foundation.org,
LKML <linux-kernel@vger.kernel.org>,
Joerg Roedel <joro@8bytes.org>,
John Garry <john.garry@huawei.com>
Subject: Re: [Patch v3 2/3] iommu: optimize iova_magazine_free_pfns()
Date: Tue, 21 Jan 2020 09:29:12 -0800 [thread overview]
Message-ID: <CAM_iQpXbjf8MuL17kZhxawXYBJm6t5-ho77F_VWR30L-9FS4Kg@mail.gmail.com> (raw)
In-Reply-To: <8ce2f5b6-74e1-9a74-fd80-9ad688beb9b2@arm.com>
On Tue, Jan 21, 2020 at 1:52 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> On 18/12/2019 4:39 am, Cong Wang wrote:
> > If the magazine is empty, iova_magazine_free_pfns() should
> > be a nop, however it misses the case of mag->size==0. So we
> > should just call iova_magazine_empty().
> >
> > This should reduce the contention on iovad->iova_rbtree_lock
> > a little bit, not much at all.
>
> Have you measured that in any way? AFAICS the only time this can get
> called with a non-full magazine is in the CPU hotplug callback, where
> the impact of taking the rbtree lock and immediately releasing it seems
> unlikely to be significant on top of everything else involved in that
> operation.
This patchset is only tested as a whole, it is not easy to deploy
each to production and test it separately.
Is there anything wrong to optimize a CPU hotplug path? :) And,
it is called in alloc_iova_fast() too when, for example, over-cached.
Thanks.
next prev parent reply other threads:[~2020-01-21 17:29 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-18 4:39 [Patch v3 0/3] iommu: reduce spinlock contention on fast path Cong Wang
2019-12-18 4:39 ` [Patch v3 1/3] iommu: avoid unnecessary magazine allocations Cong Wang
2020-01-21 11:11 ` Robin Murphy
2020-01-21 17:21 ` Cong Wang
2020-01-22 17:07 ` Robin Murphy
2020-01-22 17:54 ` Cong Wang
2019-12-18 4:39 ` [Patch v3 2/3] iommu: optimize iova_magazine_free_pfns() Cong Wang
2020-01-21 9:52 ` Robin Murphy
2020-01-21 17:29 ` Cong Wang [this message]
2020-01-22 17:34 ` Robin Murphy
2020-01-22 17:45 ` Cong Wang
2019-12-18 4:39 ` [Patch v3 3/3] iommu: avoid taking iova_rbtree_lock twice Cong Wang
2019-12-19 9:51 ` John Garry
2020-01-21 9:56 ` Robin Murphy
2020-03-03 11:33 ` John Garry
2020-01-20 23:10 ` [Patch v3 0/3] iommu: reduce spinlock contention on fast path Cong Wang
-- strict thread matches above, loose matches on Subject: below --
2019-12-06 21:38 Cong Wang
2019-12-06 21:38 ` [Patch v3 2/3] iommu: optimize iova_magazine_free_pfns() Cong Wang
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