![]() | ||||||||||
Messages in this thread |
On 12/18/06, Erik Mouw <mouw@nl.linux.org> wrote: <...snip...> > > > > But isn't O_DIRECT supposed to bypass buffering in Kernel? > > It is. > > > Doesn't it directly write to disk? > > Yes, but it still uses an IO scheduler. > Ok. but i also tried with noop to turnoff disk scheduling effects. There was still timing differences. Usually i get 3100 microseconds but upto 20000 microseconds at certain intervals. I am just using gettimeofday between two writes to read the timing. > In your first message you mentioned you were using an ancient 2.6.10 > kernel. That kernel uses the anticipatory IO scheduler. Update to the > latest stable kernel (2.6.19.1 at time of writing) and it will default > to the CFQ scheduler which has a smoother writeout, plus you can give > your process a different IO scheduling class and level (see > Documentation/block/ioprio.txt). Thanks... i will try with CFQ. Nick Piggin: > but > they look like they might be a (HZ quantised) delay coming from > block layer plugging. Sorry i didn´t understand what you mean. To minimise scheduling effects i tried giving it maximum priority. -- --------------------------------------------------------------- regards Manish Regmi --------------------------------------------------------------- UNIX without a C Compiler is like eating Spaghetti with your mouth sewn shut. It just doesn't make sense. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
| Last update: 2006-12-19 06:25 [from the cache] ©2003-2008 | ||||||||||