Messages in this thread | | | Date | Sun, 15 May 2005 23:05:52 -0400 | From | Gene Heskett <> | Subject | Re: Disk write cache (Was: Hyper-Threading Vulnerability) |
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On Sunday 15 May 2005 22:24, Mikulas Patocka wrote: >On Sun, 15 May 2005, Gene Heskett wrote: >> >There is a large amount of yammering and speculation in this >> > thread. >> >> I agree, and frankly I'm just another of the yammerers as I don't >> have the clout to be otherwise. >> >> >Most disks do seem to obey SYNC CACHE / FLUSH CACHE. >> > >> > Jeff >> >> I don't think I have any drives here that do obey that, Jeff. I >> got curious about this, oh, maybe a year back when this discussion >> first took place on another list, and wrote a test gizmo that >> copied a large file, then slept for 1 second and issued a sync >> command. No drive led activity until the usual 5 second delay of >> the filesystem had expired. To me, that indicated that the sync >> command was being returned as completed without error and I had my >> shell prompt back long before the drives leds came on. Admittedly >> that may not be a 100% valid test, but I really did expect to see >> the leds come on as the sync command was executed. >> >> I also have some setup stuff for heyu that runs at various times >> of the day, reconfigureing how heyu and xtend run 3 times a day >> here, which depends on a valid disk file, and I've had to use >> sleeps for guaranteeing the proper sequencing, where if the sync >> command actually worked, I could get the job done quite a bit >> faster. >> >> Again, probably not a valid test of the sync command, but thats >> the evidence I have. I do not believe it works here, with any of >> the 5 drives currently spinning in these two boxes. > >Note, that Linux can't send FLUSH CACHE command at all (until very > recent 2.6 kernels). So write cache is always dangerous under > Linux, no matter if disk is broken or not. > >Another note: according to posix, sync() is asynchronous --- i.e. it >initiates write, but doesn't have to wait for complete. In linux, > sync() waits for writes to complete, but it doesn't have to in > other OSes. > >Mikulas > Humm, I'm getting the impression I should rerun that test script if I can find it. I believe the last time I tried it, I was running a 2.4.x kernel, right now 2.6.12-rc1.
-- Cheers, Gene "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) 99.34% setiathome rank, not too shabby for a WV hillbilly Yahoo.com and AOL/TW attorneys please note, additions to the above message by Gene Heskett are: Copyright 2005 by Maurice Eugene Heskett, all rights reserved. - 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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