Re: [RESEND] [PATCH] readahead:add blk_run_backing_dev

[Vladislav Bolkhovitin]

Ronald Moesbergen, on 06/29/2009 02:26 PM wrote:
> 2009/6/29 Wu Fengguang <fengguang.wu@xxxxxxxxx>:
> > On Sat, Jun 20, 2009 at 08:29:31PM +0800, Vladislav Bolkhovitin wrote:
> > > Wu Fengguang, on 06/20/2009 07:55 AM wrote:
> > > > On Fri, Jun 19, 2009 at 03:04:36AM +0800, Andrew Morton wrote:
> > > > > On Sun, 7 Jun 2009 06:45:38 +0800
> > > > > Wu Fengguang <fengguang.wu@xxxxxxxxx> wrote:
> > > > >
> > > > > > > > Do you have a place where the raw blktrace data can be retrieved for
> > > > > > > > more in-depth analysis?
> > > > > > > I think your comment is really adequate. In another thread, Wu Fengguang pointed
> > > > > > > out the same issue.
> > > > > > > I and Wu also wait his analysis.
> > > > > > And do it with a large readahead size :)
> > > > > >
> > > > > > Alan, this was my analysis:
> > > > > >
> > > > > > : Hifumi, can you help retest with some large readahead size?
> > > > > > :
> > > > > > : Your readahead size (128K) is smaller than your max_sectors_kb (256K),
> > > > > > : so two readahead IO requests get merged into one real IO, that means
> > > > > > : half of the readahead requests are delayed.
> > > > > >
> > > > > > ie. two readahead requests get merged and complete together, thus the effective
> > > > > > IO size is doubled but at the same time it becomes completely synchronous IO.
> > > > > >
> > > > > > :
> > > > > > : The IO completion size goes down from 512 to 256 sectors:
> > > > > > :
> > > > > > : before patch:
> > > > > > :   8,0    3   177955    50.050313976     0  C   R 8724991 + 512 [0]
> > > > > > :   8,0    3   177966    50.053380250     0  C   R 8725503 + 512 [0]
> > > > > > :   8,0    3   177977    50.056970395     0  C   R 8726015 + 512 [0]
> > > > > > :   8,0    3   177988    50.060326743     0  C   R 8726527 + 512 [0]
> > > > > > :   8,0    3   177999    50.063922341     0  C   R 8727039 + 512 [0]
> > > > > > :
> > > > > > : after patch:
> > > > > > :   8,0    3   257297    50.000760847     0  C   R 9480703 + 256 [0]
> > > > > > :   8,0    3   257306    50.003034240     0  C   R 9480959 + 256 [0]
> > > > > > :   8,0    3   257307    50.003076338     0  C   R 9481215 + 256 [0]
> > > > > > :   8,0    3   257323    50.004774693     0  C   R 9481471 + 256 [0]
> > > > > > :   8,0    3   257332    50.006865854     0  C   R 9481727 + 256 [0]
> > > > > I haven't sent readahead-add-blk_run_backing_dev.patch in to Linus yet
> > > > > and it's looking like 2.6.32 material, if ever.
> > > > >
> > > > > If it turns out to be wonderful, we could always ask the -stable
> > > > > maintainers to put it in 2.6.x.y I guess.
> > > > Agreed. The expected (and interesting) test on a properly configured
> > > > HW RAID has not happened yet, hence the theory remains unsupported.
> > > Hmm, do you see anything improper in the Ronald's setup (see
> > > http://sourceforge.net/mailarchive/forum.php?thread_name=a0272b440906030714g67eabc5k8f847fb1e538cc62%40mail.gmail.com&forum_name=scst-devel)?
> > > It is HW RAID based.
> > No. Ronald's HW RAID performance is reasonably good.  I meant Hifumi's
> > RAID performance is too bad and may be improved by increasing the
> > readahead size, hehe.
> >
> > > As I already wrote, we can ask Ronald to perform any needed tests.
> > Thanks!  Ronald's test results are:
> >
> > 231   MB/s   HW RAID
> >  69.6 MB/s   HW RAID + SCST
> >  89.7 MB/s   HW RAID + SCST + this patch
> >
> > So this patch seem to help SCST, but again it would be better to
> > improve the SCST throughput first - it is now quite sub-optimal.
> > (Sorry for the long delay: currently I have not got an idea on
> >  how to measure such timing issues.)
> >
> > And if Ronald could provide the HW RAID performance with this patch,
> > then we can confirm if this patch really makes a difference for RAID.
>
> I just tested raw HW RAID throughput with the patch applied, same
> readahead setting (512KB), and it doesn't look promising:
>
> ./blockdev-perftest -d -r /dev/cciss/c0d0
> blocksize        W        W        W        R        R        R
>  67108864       -1       -1       -1  5.59686   5.4098  5.45396
>  33554432       -1       -1       -1  6.18616  6.13232  5.96124
>  16777216       -1       -1       -1   7.6757  7.32139   7.4966
>   8388608       -1       -1       -1  8.82793  9.02057  9.01055
>   4194304       -1       -1       -1  12.2289  12.6804    12.19
>   2097152       -1       -1       -1  13.3012   13.706  14.7542
>   1048576       -1       -1       -1  11.7577  12.3609  11.9507
>    524288       -1       -1       -1  12.4112  12.2383  11.9105
>    262144       -1       -1       -1  7.30687   7.4417  7.38246
>    131072       -1       -1       -1  7.95752  7.95053  8.60796
>     65536       -1       -1       -1  10.1282  10.1286  10.1956
>     32768       -1       -1       -1  9.91857  9.98597  10.8421
>     16384       -1       -1       -1  10.8267  10.8899  10.8718
>      8192       -1       -1       -1  12.0345  12.5275   12.005
>      4096       -1       -1       -1  15.1537  15.0771  15.1753
>      2048       -1       -1       -1   25.432  24.8985  25.4303
>      1024       -1       -1       -1  45.2674  45.2707  45.3504
>       512       -1       -1       -1  87.9405  88.5047  87.4726
>
> It dropped down to 189 MB/s. :(

Ronald,

Can you, please, rerun this test locally on the target with the latest 
version of blockdev-perftest, which produces much more readable results, 
for the following 6 cases:

1. Default vanilla 2.6.29 kernel, default parameters, including read-ahead

2. Default vanilla 2.6.29 kernel, 512 KB read-ahead, the rest is default

3. Default vanilla 2.6.29 kernel, 512 KB read-ahead, 64 KB 
max_sectors_kb, the rest is default

4. Patched by the Fengguang's patch http://lkml.org/lkml/2009/5/21/319 
vanilla 2.6.29 kernel, default parameters, including read-ahead

5. Patched by the Fengguang's patch vanilla 2.6.29 kernel, 512 KB 
read-ahead, the rest is default

6. Patched by the Fengguang's patch vanilla 2.6.29 kernel, 512 KB 
read-ahead, 64 KB max_sectors_kb, the rest is default

Thanks,
Vlad
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/