linux-kernel - Re: Intel IOMMU (and IOMMU for Virtualization) performances

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Message-Id: <20080609183125W.fujita.tomonori@lab.ntt.co.jp>
Date:	Mon, 9 Jun 2008 18:36:23 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	grundler@...gle.com
Cc:	fujita.tomonori@....ntt.co.jp,
	James.Bottomley@...senpartnership.com,
	linux-kernel@...r.kernel.org, mgross@...ux.intel.com,
	linux-scsi@...r.kernel.org, alex.williamson@...com,
	bjorn.helgaas@...com
Subject: Re: Intel IOMMU (and IOMMU for Virtualization) performances

On Thu, 5 Jun 2008 22:48:13 -0700
"Grant Grundler" <grundler@...gle.com> wrote:

> On Thu, Jun 5, 2008 at 9:44 PM, FUJITA Tomonori
> <fujita.tomonori@....ntt.co.jp> wrote:
> ...
> > The current Intel IOMMU scheme is a bit unbalanced. It invalidates the
> > translation table every time dma_unmap_* is called, but it does the
> > batching of the TLB flushes. But it's what the most of Linux's IOMMU
> > code does.
> >
> > I think that only PARISC (and IA64, of course) IOMMUs do the batching
> > of invalidating the translation table entries.
> 
> 1/2 correct. PARISC and IA64 could be the same in this regard but are not.
> See where sba_mark_invalid() is called in the respective sba_iommu.c.
> PARISC invalidates the IO Pdir entry immediately but batches the
> IO TLB shootdown and resource "free". IA64 could (and probably should)
> do the same. Added Alex Williamson and Bjorn Helgaas to CC list.
> Not an urgent issue though unless they are doing perf measurements
> with SSDs or other block device with equivalent IOPS.

Oops, thanks.

Seems that IA64 does the batching of sba_mark_invalid, sba_free_range,
and flushing TLB. IA64 and PARISC look different in this regard.
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