Qrux wrote: > On May 24, 2012, at 3:38 PM, Bruce Dubbs wrote: >> I don't think putting /boot on the ssd would make much of a difference. >> From the time I hit enter in grub to the time the kernel messages >> start is a second or less. > > Are you booting from sdc (i.e., BIOS is booting from sdc)?
Not exactly. GRUB is on sda and so is /boot. GRUB reads the linux kernel from /boot and then the kernel initializes and sets up sdc1 as the root fs. > IDK what the rest of your setup is, but IIRC, I can get to login > (after BIOS POST, etc) in about a second. I'm not sure what you mean by login here. The process is to power on (or reboot), have the BIOS do some initialization, and then run grub. The BIOS initialization (where we have no control) takes 2-3 seconds and then the GUUB prompt shows almost immediately after that. From the GRUB selection to the linux login prompt takes a lot more than one second. Just running '/sbin/udevadm trigger --action=add --type=subsystems' takes considerably more than one second. >> I then did a benchmark on rsync without the make check. When building >> on /tmp, the CMMI time was 20 seconds. When I changed the build to /mnt >> (on the ssd) the build time was 7.9 seconds. >> >> Not bad. > > Interesting data, but it might be a bit misleading to attribute all > the speedups to the SSD: > > 1) /tmp is ext3 > 2) /tmp is mounted with kernel defaults (relatime?) > 3) / is mounted with data=writeback > > 1. Ext3 is probably far worse than ext4 for CMMI tasks. Ext4 is > faster on file creation, and if it's used without barriers is going > to be much faster on writes. Obviously the tradeoff is there is > filesystem safety. > > 2. Mounted with defaults, I'd guess that ext3 is probably using > relatime. This is better than with atime enabled, but probably far > worse than noatime. IIRC, relatime still writes atime, but just less > frequently. It's still not as good as noatime. Here's a casual > write-up (with references to the epic war on LKML): > > http://tinyurl.com/2exlv7u That's an interesting discussion. > 3. That same article quotes Torvalds, IIRC, in a heated LKML on > the noatime issue: > > "But yeah, 'noatime,data=writeback' will quite likely be > *quite* noticeable (with different effects for different > loads), but almost nobody actually runs that way." > > I think the context was about filesystem safety. On a dev machine, > ext4 without barriers and data=writeback obviously makes sense. But, > it's not something I'd suggest for anyone who is concerned about the > data on the drive. > > Overall, I think the results would be more robust if you could run > the same test with ext3 with the same mount options, and see what > those results are. I created a new ext4 partition and mounted it noatime. My rsync build time was 20.3 seconds -- basically the same as ext3 with default mount options. For things like /bin and /usr, I wouldn't be particularly concerned about atime and journaling since there is little or no writing (except when doing the install part of a build). -- Bruce -- http://linuxfromscratch.org/mailman/listinfo/blfs-dev FAQ: http://www.linuxfromscratch.org/blfs/faq.html Unsubscribe: See the above information page
