On Sun, May 18, 2014 at 10:23:30AM +0200, Rolf Fokkens wrote: > Sometimes bcache_writebac task consumes 100% CPU during normal operation, but > after a while (like a minute) this drops to normal. > > It can be triggered in a reproducable fashion on my system by: > > echo 0 > /sys/block/bcache0/bcache/writeback_percent > > After this bcache_writebac starts to burn CPU cycles, and it never seems to > stop doing so. changing the writeback_percent value back to 25 doesn't change > anything. > > Apart from a busy CPU there appear to be no problem (e.g. no "task > bcache_writebac:286 blocked for more than 120 seconds" messages).
...Changing it back to 25% doesn't do anything? _that_ is odd... Can you send me the output of writeback_rate_debug? Check it once before you've done anything, when things are working normally (after a fresh boot when writeback_percent is nonzero, probably), then grab it again after you've set writeback_percent to 0 and then back to 25, when it's still spinning. There seems to be two separate bugs here, the one I'm particularly concerned about is why setting writeback_percent back to 25 doesn't restore the old behaviour. Also, what kernel are you running? -- To unsubscribe from this list: send the line "unsubscribe linux-bcache" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
