From: "Woodhouse, David" <david.woodhouse-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
To: "jroedel-l3A5Bk7waGM@public.gmane.org"
<jroedel-l3A5Bk7waGM@public.gmane.org>,
Shaohua Li <shli-b10kYP2dOMg@public.gmane.org>
Cc: "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org"
<iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org>,
"Kernel-team-b10kYP2dOMg@public.gmane.org"
<Kernel-team-b10kYP2dOMg@public.gmane.org>
Subject: Re: [PATCH 2/4] iommu: add a bitmap based dma address allocator
Date: Wed, 25 Nov 2015 16:40:00 +0000 [thread overview]
Message-ID: <1448469599.44976.134.camel@intel.com> (raw)
In-Reply-To: <20151125144613.GA3763-l3A5Bk7waGM@public.gmane.org>
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On Wed, 2015-11-25 at 15:46 +0100, jroedel-l3A5Bk7waGM@public.gmane.org wrote:
> On Tue, Nov 24, 2015 at 02:05:12PM -0800, Shaohua Li wrote:
> > The lib/iommu-common.c uses a bitmap and a lock. This implementation
> > actually uses a percpu_ida which completely avoids locking. It would be
> > possible to make lib/iommu-common.c use percpu_ida too if somebody wants
> > to do it, but I think this shouldn't be a blocker for these patches
> > giving it has huge performance gain.
>
> It doesn't "completely avoids locking", the percpu_ida code uses a lock
> internally too. Also, what is the memory and device address space
> overhead per cpu?
A percpu lock doesn't bounce cachelines between CPUs very much, so from
that point of view it might as well not exist :)
--
Sent with Evolution's ActiveSync support.
David Woodhouse Open Source Technology Centre
David.Woodhouse-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org Intel Corporation
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next prev parent reply other threads:[~2015-11-25 16:40 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-11-24 21:54 [PATCH 0/4] iommu: remove lock contention in iova allocation Shaohua Li
[not found] ` <cover.1448401089.git.shli-b10kYP2dOMg@public.gmane.org>
2015-11-24 21:54 ` [PATCH 1/4] iommu: alloc_iova returns a pfn Shaohua Li
2015-11-24 21:54 ` [PATCH 2/4] iommu: add a bitmap based dma address allocator Shaohua Li
[not found] ` <4c0804c85404be81acfe81fcd402f1af484e9d5f.1448401089.git.shli-b10kYP2dOMg@public.gmane.org>
2015-11-24 21:56 ` Woodhouse, David
[not found] ` <1448402209.44976.109.camel-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2015-11-24 22:05 ` Shaohua Li
[not found] ` <20151124220511.GA2106568-tb7CFzD8y5b7E6g3fPdp/g2O0Ztt9esIQQ4Iyu8u01E@public.gmane.org>
2015-11-25 14:46 ` jroedel-l3A5Bk7waGM
[not found] ` <20151125144613.GA3763-l3A5Bk7waGM@public.gmane.org>
2015-11-25 16:40 ` Woodhouse, David [this message]
[not found] ` <1448469599.44976.134.camel-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2015-11-25 16:43 ` Jens Axboe
[not found] ` <5655E545.1010509-b10kYP2dOMg@public.gmane.org>
2015-11-25 17:33 ` Shaohua Li
[not found] ` <20151125173320.GA92074-tb7CFzD8y5b7E6g3fPdp/g2O0Ztt9esIQQ4Iyu8u01E@public.gmane.org>
2015-11-25 17:38 ` Jens Axboe
[not found] ` <5655F1F8.9070203-b10kYP2dOMg@public.gmane.org>
2015-11-25 18:57 ` Shaohua Li
2015-11-24 21:54 ` [PATCH 3/4] iommu: enable bitmap allocation for intel iommu Shaohua Li
2015-11-24 21:54 ` [PATCH 4/4] iommu: free_iova doesn't need lock twice Shaohua Li
2015-12-07 17:52 ` [PATCH 0/4] iommu: remove lock contention in iova allocation Shaohua Li
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