Date: Tue, 13 Jul 2010 13:53:14 -0500 From: Alan Cox <alc@cs.rice.edu> To: Mark Tinguely <marktinguely@gmail.com> Cc: alc@freebsd.org, freebsd-arm@freebsd.org Subject: Re: Revision 209887 Message-ID: <4C3CB61A.1030905@cs.rice.edu> In-Reply-To: <4C3C7B4E.604@gmail.com> References: <4C3C7B4E.604@gmail.com>
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Mark Tinguely wrote: > pmap_qenter() is pretty expensive on the ARM processor with VIPT > caches, because remapping a KVA can potentially cause the shared > mappings to have their cache turned back on and then immediately > turned back off and force a cache flush. Revision 209887 makes > amd64/i386 pmap_qenter() make smart decisions on the remapping which > would help the ARM. > > Looking at the buffer code 2 or 3 weeks ago, and noticed that most of > the pmap_qenter() calls were done wisely. At that time, I was > wondering if we could/should fix the few places that involved a page > by page loop doing bogus_page substitutions and then calling > pmap_qenter() for a full buffer re-map instead of the changed page. It > appeared to me that we call pmap_qenter() L*B times where L is the > number of pages in the buffer and B is the number of bogus pages in > the buffer. We only need to change B pages. I can understand it would > not be worth the change if typically the number of pages in a buffer > and the number of bogus pages in the buffer is small. I think that vfs_unbusy_pages(), which is used exclusively by NFS, is the only remaining case. I see no reason not to change it. Go for it. Alan
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