From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kent Overstreet Subject: Re: Kernel panic with current bcache-3.2 branch. Date: Thu, 16 Aug 2012 16:36:00 -0700 Message-ID: <20120816233600.GB26564@google.com> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Joseph Glanville Cc: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org On Thu, Aug 16, 2012 at 10:07:29PM +1000, Joseph Glanville wrote: > There also seems to have been pretty severe performance regressions in > cache bypassed sequential I/O. > The newer code barely does 70mb/s sequential writes when > sequential_cuttoff is set to 4M however it does around 300mb/s when > set to 0 (no bypass) with dd and 1M block size. > When using the older codebase the cache bypass is actually slightly > faster than going to cache at around 360mb/s but this is still much > slower than the underlying block devices (as previously discussed). Ouch. Can you try profiling it with perf while running dd? perf record -afg dd etc. etc. perf report should do it