Date: Tue, 20 Jul 2010 12:10:34 -0500 From: Mark Tinguely <marktinguely@gmail.com> To: freebsd-arm@freebsd.org Cc: alc@freebsd.org Subject: Revision 209887 Message-ID: <4C45D88A.30107@gmail.com>
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This is a FYI on the pmap_qenter() change in the i386/amd64 - revision
209887.
PS to last week's email. Sorry I did not keep the message-id consistent.
A similar change in the ARM pmap_kenter_internal() seems to help
significantly. Running a port (bash3) compile on a modified GUMSTIX
kernel on an emulator, I am getting mid-teen percentages of mapping
request that we do not have to do. An example snapshot of the counts:
2475 kenter()s not needed.
11479 enters required.
All 11479 old ptes were zero because we aggressively remove dangling
allocation.
As the compilation continues, the ratio between kenter()s not needed per
kenters() needed goes up.
The numbers above assume a patch for vfs_unbusy_pages() that is the
duplicate to the one in bufdone_finish(). In theory the
vfs_unbusy_pages() should help keep the number of unnecessary
pmap_qenter() calls down, so the above numbers could only be higher
without that patch.
I also propose to removed the calls to pmap_wb_page() in pmap_qenter()
and pmap_inv_page() in pmap_qremove():
In pmap_qenter(), pmap_fix_cache() will write back the page mappings and
turn off caching if shared.
If the page was shared when pmap_qremove() is called, the caches will
already be turned off, and pmap_kremove() will writeback and invalidate
this mapping during the removal process.
--Mark.
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