On 5/29/19 12:41 AM, Paolo Valente wrote:

quoted

Il giorno 29 mag 2019, alle ore 03:09, Srivatsa S. Bhat [off-list ref] ha scritto:

On 5/23/19 11:51 PM, Paolo Valente wrote:

quoted

quoted

Il giorno 24 mag 2019, alle ore 01:43, Srivatsa S. Bhat [off-list ref] ha scritto:

When trying to run multiple dd tasks simultaneously, I get the kernel
panic shown below (mainline is fine, without these patches).

Could you please provide me somehow with a list *(bfq_serv_to_charge+0x21) ?

Hi Paolo,

Sorry for the delay! Here you go:

(gdb) list *(bfq_serv_to_charge+0x21)
0xffffffff814bad91 is in bfq_serv_to_charge (./include/linux/blkdev.h:919).
914
915	extern unsigned int blk_rq_err_bytes(const struct request *rq);
916
917	static inline unsigned int blk_rq_sectors(const struct request *rq)
918	{
919		return blk_rq_bytes(rq) >> SECTOR_SHIFT;
920	}
921
922	static inline unsigned int blk_rq_cur_sectors(const struct request *rq)
923	{
(gdb)


For some reason, I've not been able to reproduce this issue after
reporting it here. (Perhaps I got lucky when I hit the kernel panic
a bunch of times last week).

I'll test with your fix applied and see how it goes.

Great!  the offending line above gives me hope that my fix is correct.
If no more failures occur, then I'm eager (and a little worried ...)
to see how it goes with throughput :)

Your fix held up well under my testing :)

As for throughput, with low_latency = 1, I get around 1.4 MB/s with
bfq (vs 1.6 MB/s with mq-deadline). This is a huge improvement
compared to what it was before (70 KB/s).

With tracing on, the throughput is a bit lower (as expected I guess),
about 1 MB/s, and the corresponding trace file
(trace-waker-detection-1MBps) is available at:

https://www.dropbox.com/s/3roycp1zwk372zo/bfq-traces.tar.gz?dl=0

Thank you so much for your tireless efforts in fixing this issue!

Regards,
Srivatsa
VMware Photon OS