On Tue, Nov 27, 2012 at 3:38 PM, Jens Axboe <axboe@xxxxxxxxx> wrote: > On 2012-11-27 06:57, Jeff Chua wrote: >> On Sun, Nov 25, 2012 at 7:23 AM, Jeff Chua <jeff.chua.linux@xxxxxxxxx> wrote: >>> On Sun, Nov 25, 2012 at 5:09 AM, Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote: >>>> So it's better to slow down mount. >>> >>> I am quite proud of the linux boot time pitting against other OS. Even >>> with 10 partitions. Linux can boot up in just a few seconds, but now >>> you're saying that we need to do this semaphore check at boot up. By >>> doing so, it's inducing additional 4 seconds during boot up. >> >> By the way, I'm using a pretty fast SSD (Samsung PM830) and fast CPU >> (2.8GHz). I wonder if those on slower hard disk or slower CPU, what >> kind of degradation would this cause or just the same? > > It'd likely be the same slow down time wise, but as a percentage it > would appear smaller on a slower disk. > > Could you please test Mikulas' suggestion of changing > synchronize_sched() in include/linux/percpu-rwsem.h to > synchronize_sched_expedited()? Tested. It seems as fast as before, but may be a "tick" slower. Just perception. I was getting pretty much 0.012s with everything reverted. With synchronize_sched_expedited(), it seems to be 0.012s ~ 0.013s. So, it's good. > linux-next also has a re-write of the per-cpu rw sems, out of Andrews > tree. It would be a good data point it you could test that, too. Tested. It's slower. 0.350s. But still faster than 0.500s without the patch. # time mount /dev/sda1 /mnt; sync; sync; umount /mnt So, here's the comparison ... 0.500s 3.7.0-rc7 0.168s 3.7.0-rc2 0.012s 3.6.0 0.013s 3.7.0-rc7 + synchronize_sched_expedited() 0.350s 3.7.0-rc7 + Oleg's patch. Thanks, Jeff. -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
