Jens Axboe wrote:
On Mon, Jan 15 2007, Jeff Garzik wrote:
Jens Axboe wrote:
I'd be surprised if the device would not obey the 7 second timeout rule
that seems to be set in stone and not allow more dirty in-drive cache
than it could flush out in approximately that time.
AFAIK Windows flush-cache timeout is 30 seconds, not 7 as with other
commands...
Ok, 7 seconds for FLUSH_CACHE would have been nice for us too though, as
it would pretty much guarentee lower latencies for random writes and
write back caching. The concern is the barrier code, of course. I guess
I should do some timings on potential worst case patterns some day. Alan
may have done that sometime in the past, iirc.
FWIW: According to the drive guys (Eric M, among others), FLUSH CACHE
will "probably" be under 30 seconds, but pathological cases might even
extend beyond that.
Definitely more than 7 seconds in less-than-pathological cases,
unfortunately...
The SCSI layer /should/ already take this (30 second timeout) into
account, for SYNCHRONIZE CACHE (and thus FLUSH CACHE for libata) but I'm
too slack to check at the moment.
Jeff
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