* Li Zefan <lizf@xxxxxxxxxxxxxx> wrote: > >>> Lets note that this approach still has the (long existing) > >>> limitation that only one device can be block-traced at a time. > >>> > >> No, both userspace blktrace and ftrace-plugin trace can trace > >> more than one device at a time. > >> > >> # btrace /dev/sda /dev/dm-0 > >> > >> or > >> > >> # echo 1 > /sys/block/sda/trace/enable > >> # echo 1 > /sys/block/dm-0/trace/enable > > > > When they are independent - but not multiple partitions at a time: > > The only way to trace multipl partitions is to trace the whole > sda, or set trace/start_lsa and trace/end_lsa properly. ... or, once we have the filtering engine upgraded, to use or-connected filters: # [mockup example] sector >= 20000 && sector <= 30000 || sector >= 50000 && sector <= 60000 Note that users dont have to care about these expressions - they could get auto-added when tracing is enabled for a partition. Such type of more complex compound filters are possible already - what we dont have is comparison operators (right now we only have == and !=), nor built-in convenience support for dev_t. Another variant would be: dev == sda1 || dev == sda3 type of compound filters - achieving the same goal as the sector based filter. > > [root@aldebaran ~]# echo 1 > /sys/block/sda/sda1/trace/enable > > [root@aldebaran ~]# echo 1 > /sys/block/sda/sda2/trace/enable > > -bash: echo: write error: Device or resource busy > > That's because struct blk_trace is attached to struct > request_queue, sda1 and sda2 share the same rq: > > # echo 1 > /sys/block/sda/sda1/trace/enable > # cat /sys/block/sda/sda1/trace/enable > 1 > # cat /sys/block/sda/sda2/trace/enable > 1 yes - i'm just pointing out the limitation. It's no big issue currently - most of the actual tracing happens on specific devices/partitions. (Perhaps 'whole system blk tracing' is a common pattern though.) I'm just pointing out that this is a beauty wart, and that it will be mostly addressed when we go to TRACE_EVENT() based tracepoints in blktrace :-) Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-btrace" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
