Hello, I was investigating a performance issue with BFQ IO scheduler and I was pondering why I'm not seeing informational messages from BFQ. After quite some debugging I have found out that commit 35fe6d763229 "block: use standard blktrace API to output cgroup info for debug notes" broke standard blktrace API - namely the informational messages logged by bfq_log_bfqq() are no longer displayed by blkparse(8) tool. This is because these messages have now __BLK_TA_CGROUP bit set and that breaks flags checking in blkparse(8). It isn't that hard to fix blkparse once you know what the problem is but I've wasted couple hours on this... Also apparently nobody tested the patch with blkparse(8) since 4.14 days? Admittedly this requires CONFIG_BFQ_GROUP_IOSCHED and having cgroups set up for the cgroup info to get emitted which probably is not that common with non-production machines. Anyway, what to do now? Update blkparse(8) and hope nobody else is using the blktrace API (likely I'd say)? Revert the change? Honza -- Jan Kara <jack@xxxxxxxx> SUSE Labs, CR
