From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Mark Lord <liml@rtr.ca>
Cc: Jeff Garzik <jgarzik@pobox.com>, Tejun Heo <htejun@gmail.com>,
Alan Cox <alan@redhat.com>,
James Bottomley <James.Bottomley@HansenPartnership.com>,
IDE/ATA development list <linux-ide@vger.kernel.org>,
FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Subject: Re: libata .sg_tablesize: why always dividing by 2 ?
Date: Wed, 27 Feb 2008 08:50:49 +1100 [thread overview]
Message-ID: <1204062649.15052.164.camel@pasglop> (raw)
In-Reply-To: <47C4439E.2000606@rtr.ca>
On Tue, 2008-02-26 at 11:51 -0500, Mark Lord wrote:
> > That's interesting. Can you point us to the exact file::lines where
> > this happens? It would be good to ensure that this gets fixed.
> >
> > I'm copying Fujita Tomonori on this thread now -- he's the dude
> who's
> > trying to sort out the IOMMU mess.
> ..
>
> Mmm.. looks like ppc is already fixed in mainline,
> commit 740c3ce66700640a6e6136ff679b067e92125794
No, I only fixed alignent up to PAGE_SIZE, not above.
Our iommu can use smaller than PAGE_SIZE allocations when PAGE_SIZE is
64k (it can use 4k), and that helps a lot with networking to avoid
filling up pSeries small iommu's too fast. Unfortunately, that meant we
used to not even get PAGE_SIZE alignment for some cases. The workaround
fixes that but does not provide natural size alignment.
If we were to provide size based alignment of sg requests, fragmentation
would become so bad we would basically end up failing a large amount of
iommu allocations on servers.
Ben.
next prev parent reply other threads:[~2008-02-26 22:11 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2008-02-26 0:02 libata .sg_tablesize: why always dividing by 2 ? Mark Lord
2008-02-26 0:15 ` Jeff Garzik
2008-02-26 0:27 ` Mark Lord
2008-02-26 0:54 ` Benjamin Herrenschmidt
2008-02-26 1:37 ` Mark Lord
2008-02-26 1:43 ` Mark Lord
2008-02-26 2:54 ` Benjamin Herrenschmidt
2008-02-26 4:38 ` Mark Lord
2008-02-26 5:30 ` Benjamin Herrenschmidt
2008-02-26 5:43 ` Mark Lord
2008-02-26 5:47 ` Benjamin Herrenschmidt
2008-02-26 16:09 ` James Bottomley
2008-02-26 21:43 ` Benjamin Herrenschmidt
2008-02-26 16:25 ` Mark Lord
2008-02-26 16:51 ` Mark Lord
2008-02-26 21:50 ` Benjamin Herrenschmidt [this message]
2008-02-26 21:56 ` James Bottomley
2008-02-26 22:30 ` Benjamin Herrenschmidt
2008-02-26 23:16 ` Benjamin Herrenschmidt
2008-02-26 21:43 ` Benjamin Herrenschmidt
2008-02-26 23:07 ` Alan Cox
2008-02-26 23:19 ` Benjamin Herrenschmidt
2008-02-28 7:36 ` FUJITA Tomonori
2008-02-28 7:44 ` Benjamin Herrenschmidt
2008-02-26 2:52 ` Benjamin Herrenschmidt
2008-02-26 0:22 ` Jeff Garzik
2008-02-26 0:28 ` Mark Lord
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