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Message-ID: <20100817182920.GD18161@basil.fritz.box> Date: Tue, 17 Aug 2010 20:29:20 +0200 From: Andi Kleen <andi@...stfloor.org> To: "J. Bruce Fields" <bfields@...ldses.org> Cc: Andi Kleen <andi@...stfloor.org>, "Patrick J. LoPresti" <lopresti@...il.com>, linux-fsdevel@...r.kernel.org, linux-nfs@...r.kernel.org, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: Proposal: Use hi-res clock for file timestamps > OK, so that leaves us with the race, even on newer filesystems: > > 1. File is modified, mtime updated > 2. Client fetches mtime to revalidate cache > 3. File is modified again, mtime updated > 4. Client fetches new mtime to revalidate cache You'll always have a race window with time, the only way around that would be a version number. > - Tell everyone to use NFSv4 (and make sure we have > changeattr/i_version working correctly). > - Use a finer-grained time source. (I believe you when you say > the TSC is too slow, but maybe we should run some tests to > make sure.) It depends on the CPU too. > - Increment mtime by a nanosecond when necessary. You cannot be more precise than the backing file system: this causes non monotonity when the inodes are flushed (has happened in the past) -Andi -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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