Sounds like a good portion of your IO is bypassing the cache. That will happen if some of it's sequential, or if the SSD latency goes over a threshold - sequential_cutoff, congested_read_threshold_us and congest_write_threshold_us (if I'm remembering the names correctly) are the settings that control all that. 0 disables all of them.
On Wed, Sep 12, 2012 at 1:01 PM, Brad Walker <[email protected]> wrote: > I am having a problem with BCache. > > I’ve followed the documentation and have my cache attached. Here is > what dmesg tells me: > > [ 372.622905] bcache: invalidating existing data > [ 372.637517] bcache: registered cache device rssda1 > [ 400.704672] bcache: Caching dm-2 as bcache0 on set > 16fd7139-f018-461c-9d9e-daa > > I warmed up the cache by using an application (vdbench) to do random > reads over a 10GB region. > > Everything looks good as the response time comes down as the cache > warms up. But, for some reason the cache_hit_rate is showing 90% and > yet I’m still seeing heavy activity to the disk device. > > bwalker@nellis:~> cat > /sys/fs/bcache/16fd7139-f018-461c-9d9e-daa7666c7f1e/stats_total/cache_hit_ratio > 94 > bwalker@nellis:~> > > Any ideas on why this might be happening are appreciated. > > -brad w. > -- > 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 -- 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
