On 12/06/18 17:09, Jens Axboe wrote: > On 6/12/18 9:38 AM, Chris Boot wrote: >> Hi folks, >> >> I maintain a large (to me) system with 112 threads (4x Intel E7-4830 v4) >> which has a MegaRAID SAS 9361-24i controller. This system is currently >> running Debian's 4.16.12 kernel (from stretch-backports) with blk_mq >> enabled. >> >> I've run into a lockup which appears to involve blq_mq and writeback >> throttling. It's hard to tell if I've run into this same thing with >> older kernels; I'm trying to track down a deadlock but so far I've been >> fairly certain that involved the OOM killer, but this doesn't seem to. [snip] > > Hmm that's really weird, I don't see how we could be spinning on the > waitqueue lock like that. I haven't seen any wbt bug reports like this > before. > > Are things generally stable if you just turn off wbt? You can do that > for sda, for instance, by doing: > > # echo 0 > /sys/block/sda/queue/wbt_lat_usec > > It'd be interesting to get this data point. Eg leave blk-mq enabled, and > then just disable wbt. Hi Jens, Thanks for the speedy response. I'll see if I can get that tested soon; if the system is stable without blk_mq I can see the users wanting to keep it that way for a while. I'll let you know. > Is anything disabling wbt in the system otherwise? Not that I'm aware of, no. Thanks, Chris -- Chris Boot bootc@xxxxxx
