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In message <20020511142434.GA1224@suse.de>, > : Jens Axboe writes: > On Sat, May 11 2002, Roy Sigurd Karlsbakk wrote: > > On Friday 10 May 2002 17:55, Linus Torvalds wrote: > > > On Fri, 10 May 2002, Lincoln Dale wrote: > > > > so O_DIRECT in 2.4.18 still shows up as a 55% performance hit versus no > > > > O_DIRECT. anyone have any clues? > > > Yes. > > > > > > O_DIRECT isn't doing any read-ahead. > > > > > > For O_DIRECT to be a win, you need to make it asynchronous. > > > > Will the use of O_DIRECT affect disk elevatoring? > > No, the I/O scheduler can't even tell whether it's being handed > O_DIRECT buffers or not. We tried disabling the elevator while doing Raw IO with DB2 a couple of weeks ago. The database performance degraded much more than expected. Disks were FC connected Tritons or SCSI connected ServerRaid (or both?). Oracle often asks for a patch to disable the elevator since they believe they can schedule IO better. We didn't try with Oracle in this case, but DB2 and RAW IO without and elevator was not a good choice. gerrit - 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/ | ||||||||||||
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