From: Jesse Barnes <jbarnes@virtuousgeek.org>
To: Eric Anholt <eric@anholt.net>
Cc: lkml <linux-kernel@vger.kernel.org>,
Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Subject: Re: PAGE_CACHE_WC strikes again
Date: Tue, 31 Mar 2009 17:14:31 -0700 [thread overview]
Message-ID: <20090331171431.69ad044f@hobbes> (raw)
In-Reply-To: <1238544647.8369.682.camel@gaiman.anholt.net>
On Tue, 31 Mar 2009 17:10:47 -0700
Eric Anholt <eric@anholt.net> wrote:
> I just tracked down what was cutting performance 10x on one of my
> systems on a microbenchmark I'd just written:
>
> --- a/drivers/gpu/drm/drm_gem.c
> +++ b/drivers/gpu/drm/drm_gem.c
> @@ -540,7 +540,7 @@ int drm_gem_mmap(struct file *filp, struct
> vm_area_struct *vma)
> /* FIXME: use pgprot_writecombine when available */
> prot = pgprot_val(vma->vm_page_prot);
> #ifdef CONFIG_X86
> - prot |= _PAGE_CACHE_WC;
> + /*prot |= _PAGE_CACHE_WC;*/
> #endif
> vma->vm_page_prot = __pgprot(prot);
>
> Turns out that setting PAGE_CACHE_WC disables the WC effect of the
> MTRR on my non-PAT (disabled due to CPU errata) 945GM system, and this
> workaround took GTT-mapped writes from 120MB/s to 1180MB/s.
What the... There's a pgprot_writecombine now, but it basically does
the same thing. Why is WC so broken? Venki is the fix for this
covered in your last patchset?
--
Jesse Barnes, Intel Open Source Technology Center
next prev parent reply other threads:[~2009-04-01 0:15 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-04-01 0:10 Eric Anholt
2009-04-01 0:14 ` Jesse Barnes [this message]
2009-04-01 0:29 ` Pallipadi, Venkatesh
2009-04-01 0:49 ` Jesse Barnes
2009-04-01 1:03 ` Suresh Siddha
2009-04-01 1:12 ` Jesse Barnes
2009-04-01 1:30 ` Suresh Siddha
2009-04-01 1:57 ` Jesse Barnes
2009-04-01 3:18 ` Dave Airlie
2009-04-01 3:17 ` Pallipadi, Venkatesh
2009-04-01 1:22 ` Jesse Barnes
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