Date: Sat, 18 Feb 2006 08:50:17 +0530 From: "Joseph Koshy" <joseph.koshy@gmail.com> To: "Andrew Gallatin" <gallatin@cs.duke.edu> Cc: freebsd-amd64@freebsd.org Subject: Re: non-temporal copyin/copyout? Message-ID: <84dead720602171920y153bd9d5p1c0aa11cbc177020@mail.gmail.com> In-Reply-To: <17397.63064.242130.484086@grasshopper.cs.duke.edu> References: <17397.58669.457047.277510@grasshopper.cs.duke.edu> <84dead720602170750j119080c9g32ec9f1ac0e3944d@mail.gmail.com> <17397.63064.242130.484086@grasshopper.cs.duke.edu>
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On 2/17/06, Andrew Gallatin <gallatin@cs.duke.edu> wrote:
ag> "k8-dc-miss" : data cache misses
ag> 91.5 6466.00 6466.00 0 100.00% copyout [1]
ag> "k8-bu-fill-request-l2-miss,mask=3Ddc-fill" : L2 fills
ag> for the data cache
ag> 88.2 3866.00 3866.00 0 100.00% copyout [1]
Certainly copyout() appears to be thrashing the cache.
ag> "k8-dc-misaligned-data-reference": in case there are any
ag> 99.5 66763.00 66763.00 0 100.00% copyout [1]
The code in question "/usr/src/sys/amd64/amd64/support.S" has:
216 ENTRY(copyout)
...
249 shrq $3,%rcx
250 cld
251 rep
252 movsq
253 movb %dl,%cl
254 andb $7,%cl
255 rep
256 movsb
i.e., it doesn't handle the case where the `from_kernel'
or `to_user' addresses are misaligned to their natural
boundaries. IIRC `rep movsq' works best if both the source
and destination addresses are 8-byte aligned.
If we are going to use `movntq' then we may as well take
care of alignment issues too.
jk> "k8-fr-interrupts-masked-while-pending-cycles": for
jk> finding spots in the code where spin-locks are being
jk> held for long.
ag> I had to tweak the sample rate to 512 for this one.
ag> 52.5 330.00 330.00 0 100.00% acpi_cpu_idle [1]
ag> 10.4 395.00 65.00 0 100.00% spinlock_exit [2]
ag> 9.1 452.00 57.00 0 100.00% acpi_cpu_c1 [3]
This is interesting too, but I'm not sure how much of
an effect it has on this particular benchmark.
--
FreeBSD Volunteer, http://people.freebsd.org/~jkoshy
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