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Date: Thu, 8 Aug 2013 05:11:54 -0700 From: Christoph Hellwig <hch@...radead.org> To: Kent Overstreet <kmo@...erainc.com> Cc: Christoph Hellwig <hch@...radead.org>, Ben Hutchings <ben@...adent.org.uk>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org, Uwe Kleine-K?nig <u.kleine-koenig@...gutronix.de> Subject: Re: PREEMPT_RT vs bcache On Thu, Aug 08, 2013 at 12:43:26AM -0700, Kent Overstreet wrote: > I seem to recall from looking at the logs that you just removed them > because all the old users could be and were converted to something > saner, for what they were doing (using them as completions, I want to > say?) We explicitly converted them away so that we could kill it. This was a joint project with Thomas. > Bcache isn't using the rw sem as a completion though, it really is a > read/write lock that protects a specific data structure, and where > we're taking a read lock for the duration of write IOs - and since bios > are asynchronous, that's why we need the non_owner() bit. Part of this commit was to make the rw_semaphore behaviour similar to plain mutex, that is making sure there is exactly one owner and not different processes locking/unlocking it. This is useful for PI (that's why the rt folks care), lock debugging and kinds of other use cases. -- 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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