From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Priebe - Profihost AG Subject: Re: bcache kernel 3.10 wrong bypassed values Date: Fri, 12 Jul 2013 13:18:35 +0200 Message-ID: <51DFE60B.6040701@profihost.ag> References: <51D52EA0.80302@profihost.ag> <20130712015559.GF17799@kmo-pixel> <51DF9E90.8070408@profihost.ag> <20130712082031.GC8339@kmo-pixel> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20130712082031.GC8339@kmo-pixel> Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Kent Overstreet Cc: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org Am 12.07.2013 10:20, schrieb Kent Overstreet: > On Fri, Jul 12, 2013 at 08:13:36AM +0200, Stefan Priebe - Profihost AG wrote: >> Am 12.07.2013 03:55, schrieb Kent Overstreet: >>> On Thu, Jul 04, 2013 at 10:13:20AM +0200, Stefan Priebe - Profihost AG wrote: >>>> Hello list, >>>> >>>> while testing bcache i noticed that while writing a big 48GB file the >>>> sequential cutoff works fine i see only I/O on the disk but not on the >>>> cache. I thought i would afterwards see a bypassed value of around 48GB >>>> but it is only 1.2GB. >>>> >>>> Is this expected? Is bcache in kernel 3.10 stable for production usage? >>> >>> That sounds like a bug, but bcache in 3.10 certainly should be stable >>> for production usage. >>> >>> There can be some weirdness due to the way the stats work, there's a ~13 >>> second update interval (and also the intermediate counters are 32 bit >>> ints so if you manage to wrap that in 13 seconds you'll lose counts, but >>> it's counting sectors so I doubt that happened here). >> >> Mhm i doubt that too. But if i write 40GB shouldn't i see a bypass value >> near 40GB? It's just very small. >> >>> Does that sound like it might explain what you were seeing, or do you >>> think there's something else going on? >> No right no i don't believe that. > > Have you noticed any pattern to it? Does it appear to sometimes be right > and sometimes wrong, or is it always wrong? It seems that the dirty stats starts with 0 after a reboot but there might still be some dirty data in it? > I looked again at the code that updates that value and I'm not coming up > with any ideas to explain what you're seeing... Output: Rawdisk: /dev/sde1 (rawdisk10) | Cachedisk: /dev/sdb4 (bcachessd2) Read MB/s | Write MB/s | Read MB/s | Write MB/s | Dirty | Bypassed (op/s) | (op/s) | (op/s) | (op/s) | | 0.00 ( 0) | 18.45 ( 119) | 5.57 ( 58) | 6.06 ( 60) | -16.3M | 68.9M 0.00 ( 0) | 0.00 ( 7) | 0.01 ( 2) | 7.10 ( 39) | -12.5M | 68.9M 0.00 ( 1) | 0.00 ( 4) | 0.06 ( 8) | 23.29 ( 100) | -3.1M | 67.9M 0.00 ( 0) | 0.00 ( 7) | 0.04 ( 8) | 21.43 ( 82) | 9.5M | 67.9M 0.04 ( 8) | 0.00 ( 3) | 0.02 ( 3) | 4.81 ( 73) | 11.0M | 67.9M 0.00 ( 0) | 0.64 ( 12) | 0.02 ( 5) | 19.68 ( 139) | 26.9M | 67.9M 0.00 ( 0) | 0.00 ( 5) | 0.02 ( 4) | 4.61 ( 36) | 31.4M | 67.9M Stefan