lkml.org 
[lkml]   [2008]   [Jan]   [19]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] LatencyTop: make reason (blk_execute_rq+0x7a/0xd) known
Török Edwin wrote:
> Hi Arjan,
>
> One of the top reasons in latencytop is
> Unknown reason (blk_execute_rq+0x7a/0xd) 152.3 msec
> 49.0 msec
>
> Its from hddtemp, hald-addon-storage, ...
>
> I wrote a simple systemtap script [1] to find out where its called from,
> and its definitely from the ioctl (see below).
>
> 1820322406
> hddtemp(3999):
> <- latency of 153260223 ns
> Returning from: 0xffffffff80311ab0 : blk_execute_rq+0x0/0xd0 []
> Returning to : 0xffffffff80315580 : sg_io+0x200/0x3c0 []
> 0xffffffff80315a02 : scsi_cmd_ioctl+0x2c2/0x410 []
> 0xffffffff80417153 : ip_queue_xmit+0x2b3/0x420 []
> 0xffffffff880c3be9 : sd_ioctl+0x99/0xf0 [sd_mod]
> 0xffffffff80313839 : blkdev_driver_ioctl+0x39/0x40 []
> 0xffffffff80313ab8 : blkdev_ioctl+0x278/0x710 []
> 0xffffffff803e540d : release_sock+0x8d/0xa0 []
> 0xffffffff803e54b3 : lock_sock_nested+0x93/0xa0 []
> 0xffffffff8029a4ff : d_alloc+0x6f/0x1a0 []
> 0xffffffff802f102f : security_d_instantiate+0x1f/0x30 []
> 0xffffffff803e540d : release_sock+0x8d/0xa0 []
> 0xffffffff8043c8c8 : inet_accept+0x88/0xc0 []
> 0xffffffff803e408e : move_addr_to_user+0x5e/0x70 []
> 0xffffffff802f0bb1 : security_socket_post_accept+0x11/0x20 []
> 0xffffffff803e472e : sys_accept+0x13e/0x1d0 []
> 0xffffffff802af12b : block_ioctl+0x1b/0x20 []
> 0xffffffff8029482b : do_ioctl+0x1b/0x70 []
> 0xffffffff80294a6d : vfs_ioctl+0x1ed/0x290 []
> 0xffffffff80296281 : sys_select+0x41/0x1b0 []
> 0xffffffff80294b92 : sys_ioctl+0x82/0xa0 []
> 0xffffffff8020c18e : system_call+0x7e/0x83 []
>
>
> I suggest adding an annotation to make this reason known to latencytop
> by annotating sd_ioctl/scsi_cmd_ioctl, see my patch below.
> After my patch, instead of blk_execute_rq the real reason is showed:
>
> Cause Maximum Average
> SCSI device ioctl 34.2 msec
> 14.4 msec

great! I'll put this into my patchkit!

>
> I noticed there's a similar annotation in sr.c for cdrom_ioctl, but sr.c
> also has annotations for scsi_nonblockable_ioctl, and scsi_ioctl.
> If they are needed for sd_block_ioctl too, maybe
> scsi_nonblockable_ioctl/scsi_ioctl should have the annotation themselves.

yeah I'll take a look at this; some of the annotations are still a bit iffy in their placement

>
> I also noticed some unsigned overflows, my top latency was sometimes a
> very large number (18................................), which
> was probably -1, or some other negative number. I haven't found a way
> to reproduce it yet (it happens very rarely).

I've not seen this; I'll take another peak at the code.

> P.S.: LatencyTop could have a feature to ask for more details on unknown
> latency reasons, and it would generate a systemtap script itself, that
> would show the backtraces to help figure out whats going on.

I've considered having an option inside the code itself that would print a
backtrace for, say, an unknown latency larger than 100msec
but the code got ugly (the accounting gets done in the scheduler path,
where you can't printk).
I'll try again ;-)
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2008-01-19 19:33    [W:0.928 / U:1.092 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site