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Message-ID: <20130515054353.GO29466@dastard> Date: Wed, 15 May 2013 15:43:53 +1000 From: Dave Chinner <david@...morbit.com> To: Jan Kara <jack@...e.cz> Cc: "Sidorov, Andrei" <Andrei.Sidorov@...isi.com>, ext4 development <linux-ext4@...r.kernel.org> Subject: Re: Barriers On Tue, May 14, 2013 at 11:41:58PM +0200, Jan Kara wrote: > Hi, > > On Mon 13-05-13 07:54:48, Sidorov, Andrei wrote: > > I'm curious if anyone ever tried fua-only jbd? If done with fua's, there > > will be no cache flushes at all, thus no occasional spikes. NCQ fua > > journalling is potentially more efficient than cache flush. > If you have such HW, it may be an interesting thing to try. Be careful there - you still need to guarantee all metadata that is being overwritten in the log has been flushed to stable storage, so even when you are using FUA for the journal writes you still need a pre-write flush to occur. Another tricky case here is that if you are using an external log, the flush needs to occur on the metadata device, not the log device, and it needs to complete before you submit the FUA journal write. Cheers, Dave. -- Dave Chinner david@...morbit.com -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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