http://bugzilla.kernel.org/show_bug.cgi?id=10846 ------- Comment #3 from dom.lalot@xxxxxxxxx 2008-06-03 00:00 ------- James and Roland Sure there's write cache enabled and your remark make sense. That's the first thing I noticed when changing kernel. We went from 2.8.18 SCSI device sda: drive cache: write through SCSI device sda: 285155328 512-byte hdwr sectors (146000 MB) testing with kernels 2.6.22 or 2.6.24, we noticed a change about the write cache, just changing the kernel on the same hardware. [ 115.986031] sd 4:1:0:0: [sdb] Write cache: disabled, read cache: enabled, doesn't support DPO or FUA [ 115.986494] sd 4:1:0:0: [sdb] 285155328 512-byte hardware sectors (146000 MB) So we got a utility lsiutil to change the settings in the firmware about write cache, and we saw then write cache: enabled, but the speed stayed slow. We also took a driver from lsi About your remarks, I tested again using dd with a larger file (when untaring the kernel there's also a difference but it is less basic than dd) The way dd reports its speed may be not very accurate I agree, but it does not change from a kernel point of view. Linux debian-test.pr.univmed.fr 2.6.21.7 debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=100000 100000+0 enregistrements lus 100000+0 enregistrements écrits 1024000000 octets (1,0 GB) copiés, 5,39271 seconde, 190 MB/s debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=100000 100000+0 enregistrements lus 100000+0 enregistrements écrits 1024000000 octets (1,0 GB) copiés, 5,45364 seconde, 188 MB/s debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=200000 200000+0 enregistrements lus 200000+0 enregistrements écrits 2048000000 octets (2,0 GB) copiés, 23,0492 seconde, 88,9 MB/s debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=200000 200000+0 enregistrements lus 200000+0 enregistrements écrits 2048000000 octets (2,0 GB) copiés, 22,5306 seconde, 90,9 MB/s I reboot and change kernel: debian-test:~# uname -a Linux debian-test.pr.univmed.fr 2.6.22.19 #1 SMP Fri May 30 19:53:56 CEST 2008 i686 GNU/Linux debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=100000 100000+0 enregistrements lus 100000+0 enregistrements écrits 1024000000 octets (1,0 GB) copiés, 13,9614 seconde, 73,3 MB/s debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=100000 100000+0 enregistrements lus 100000+0 enregistrements écrits 1024000000 octets (1,0 GB) copiés, 13,9406 seconde, 73,5 MB/s debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=200000 200000+0 enregistrements lus 200000+0 enregistrements écrits 2048000000 octets (2,0 GB) copiés, 29,3472 seconde, 69,8 MB/s debian-test:~# dd if=/dev/zero of=/root/test.cdrom bs=10k count=200000 200000+0 enregistrements lus 200000+0 enregistrements écrits 2048000000 octets (2,0 GB) copiés, 29,1689 seconde, 70,2 MB/s debian-test:~# (I believe that, if I take a bigger file, we will get the same speed, the difference is due to the first data going to write cache) What can we see: 1. having a larger file make the write cache less efficient (normal) 2. It seems that the write caching is no more working from 2.6.22 on our hardware (new blade servers from Dell m600). Even using firmware utilities didn't improve the speed. LSI firmware does not activate write cache and their BIOS has no setup for that. Switching from 2.6.18 to 2.6.22 makes the kernel no more doing write cache. Changing in the firmware activate something.. just in dmesg, we see it: enabled again, but in fact there's no speed difference. My subject should have been: no more write caching -- Configure bugmail: http://bugzilla.kernel.org/userprefs.cgi?tab=email ------- You are receiving this mail because: ------- You are the assignee for the bug, or are watching the assignee. -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
