On Sat, May 28, 2011 at 12:03 PM, Pieter de Goeje <pie...@degoeje.nl> wrote: > On Friday 13 May 2011 20:48:01 Matthew D Fleming wrote: >> Author: mdf >> Date: Fri May 13 18:48:00 2011 >> New Revision: 221853 >> URL: http://svn.freebsd.org/changeset/base/221853 >> >> Log: >> Usa a globally visible region of zeros for both /dev/zero and the md >> device. There are likely other kernel uses of "blob of zeros" than can >> be converted. >> >> Reviewed by: alc >> MFC after: 1 week >> > > This change seems to reduce /dev/zero performance by 68% as measured by this > command: dd if=/dev/zero of=/dev/null bs=64k count=100000. > > x dd-8-stable > + dd-9-current > +-------------------------------------------------------------------------+ > |+ | > |+ | > |+ | > |+ x x| > |+ x x x| > |A |MA_|| > +-------------------------------------------------------------------------+ > N Min Max Median Avg Stddev > x 5 1.2573578e+10 1.3156063e+10 1.2827355e+10 1.290079e+10 2.4951207e+08 > + 5 4.1271391e+09 4.1453925e+09 4.1295157e+09 4.1328097e+09 7487363.6 > Difference at 95.0% confidence > -8.76798e+09 +/- 2.57431e+08 > -67.9647% +/- 1.99547% > (Student's t, pooled s = 1.76511e+08) > > This particular measurement was against 8-stable but the results are the same > for -current just before this commit. Basically througput drops from > ~13GB/sec to 4GB/sec. > > Hardware is a Phenom II X4 945 with 8GB of 800Mhz DDR2 memory. FreeBSD/amd64 > is installed. This processor has 6MB of L3 cache. > > To me it looks like it's not able to cache the zeroes anymore. Is this > intentional? I tried to change ZERO_REGION_SIZE back to 64K but that didn't > help.
Hmm. I don't have access to my FreeBSD box over the weekend, but I'll run this on my box when I get back to work. Meanwhile you could try setting ZERO_REGION_SIZE to PAGE_SIZE and I think that will restore things to the original performance. Cheers, matthew _______________________________________________ svn-src-head@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/svn-src-head To unsubscribe, send any mail to "svn-src-head-unsubscr...@freebsd.org"
