Messages in this thread | | | Date | Mon, 5 Sep 2011 17:37:58 +0200 | From | Jan Kara <> | Subject | Re: Abysmal I/O scheduling with dm-crypt |
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Hello,
On Tue 30-08-11 09:14:07, martin f krafft wrote: > for years I have been plagued by the following problem, and it is > almost out of last resort that I am turning to you. I have searched > the web over the months. There is talk of dirty_ratios, of caches, > and of write throttling, but I have not been able to find a way to > fix the problem. > > I am using encrypted filesystems (dm-crypt) and the 3.0.0 kernel. > Underneath might be a RAID1 or a fast SSD. On top is usually LVM > with a few LVs holding the system. > > Whenever an I/O-intensive task starts, such as: > > - tar -c or -x > - dd > - rsync > - notmuch > - … > > the system becomes unusable for several seconds at a time, at least > once or twice per minute. What seems to happen is that Vim or the > Shell or Firefox or whatever else completely blocks, waiting for > I/O, but Linux is not satisfying those I/O requests because it's > busy servicing the aforementioned I/O-intensive task. As a result, > Vim or the Shell or Firefox or whatever do not update, forcing me to > wait for them to get an I/O service slot. > > People not running dm-crypt seem unable to reproduce this problem, > making me think that it must be due to dm-crypt, and I wouldn't find > it hard to imagine, because dm-crypt basically shields the > I/O-scheduler of the kernel, doesn't it? Worse, it probably doesn't > make any effort of scheduling I/O itself. Note: I know very little > about the internals, so please correct me if I am wrong. > > I am wondering if this is the case, and if so, what could be done > about it. So as a start can you provide blktrace of all the relevant devices (i.e. underlying SATA drive and dm-crypt device)? I.e. on my machine with dm-crypt I'd run blktrace -d /dev/sda -d /dev/mapper/cr_sda3
Also periodically getting list of blocked processes like while true; do ps axl | grep " D"; echo "------"; usleep 100000; done might sched some light.
Honza -- Jan Kara <jack@suse.cz> SUSE Labs, CR -- 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/
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