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SubjectRe: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data"
On Fri, Sep 13, 2013 at 11:38:04AM +0800, Fengguang Wu wrote:
> On Thu, Sep 12, 2013 at 08:17:00PM -0700, Greg KH wrote:
> > On Fri, Sep 13, 2013 at 08:51:33AM +0800, Fengguang Wu wrote:
> > > Hi Peter,
> > >
> > > FYI, we noticed much increased vmap_area_lock contentions since this
> > > commit:
> >
> > What does that mean? What is happening, are we allocating/removing more
> > memory now?
>
> // leave this question to Peter and Tejun. :)
>
> > What type of load were you running that showed this problem?
>
> The increased contentions and lock hold/wait time showed up in a
> number of test cases.
>
> The second email has the details, and this section of data is most
> illustrating.
>
> 8cb06c983822103da1cf 20bafb3d23d108bc0a89
> ------------------------ ------------------------
> 3470.31 +1631.0% 60070.49 fat/micro/dd-write/1HDD-cfq-ext4-10dd
> 3339.57 +1676.9% 59340.71 fat/micro/dd-write/1HDD-cfq-ext4-1dd
> 2848.79 +1489.1% 45269.54 lkp-a04/micro/netperf/120s-200%-TCP_CRR
> 3563.01 +1515.2% 57548.50 lkp-a04/micro/netperf/120s-200%-TCP_MAERTS
> 2678.64 +1346.0% 38733.80 lkp-a04/micro/netperf/120s-200%-TCP_RR
> 2839.84 +1450.2% 44022.08 lkp-a04/micro/netperf/120s-200%-TCP_SENDFILE
> 3417.37 +1571.4% 57116.34 lkp-a04/micro/netperf/120s-200%-TCP_STREAM
> 2558.59 +1450.8% 39677.58 lkp-a04/micro/netperf/120s-200%-UDP_RR
> 3737.24 +1558.0% 61963.62 lkp-a04/micro/netperf/120s-200%-UDP_STREAM
> 20219.50 +1488.7% 321218.02 lkp-a06/crypto/tcrypt/2s-200-204
> 21017.17 +1457.1% 327257.41 lkp-a06/crypto/tcrypt/2s-205-210
> 22109.84 +1240.3% 296346.33 lkp-a06/crypto/tcrypt/2s-401-417
> 17909.60 +1467.3% 280693.71 lkp-a06/micro/dbench/100%
> 489739.50 +978.5% 5281916.05 lkp-ne04/micro/aim7/shell_rtns_1
> 1601675.63 +906.7% 16123642.52 lkp-snb01/micro/aim7/exec_test
> 12105.00 +2453.6% 309110.42 nhm-white/micro/aim7/dbase
> 822461.02 +1585.0% 13858430.62 nhm-white/micro/aim7/exec_test
> 9858.11 +2715.9% 277595.41 nhm-white/micro/aim7/fork_test
> 3452.91 +1685.5% 61650.74 nhm-white/micro/aim7/fserver
> 300.14 +2621.5% 8168.53 nhm-white/micro/aim7/misc_rtns_1
> 345479.21 +1624.5% 5957828.25 nhm-white/micro/aim7/shell_rtns_1
> 2694.48 +1974.4% 55894.19 nhm-white/sysbench/oltp/100%-600-1000000
> 4415.67 +1202.2% 57501.52 nhm8/micro/dbench/100%
> 2284.65 +1505.2% 36672.75 snb-drag/crypto/tcrypt/2s-200-204
> 2446.02 +1537.1% 40042.87 snb-drag/crypto/tcrypt/2s-205-210
> 2484.11 +1599.6% 42219.71 snb-drag/crypto/tcrypt/2s-500-504
> 2118.55 +1155.8% 26604.99 vpx/crypto/tcrypt/2s-200-204
> 2713.48 +1198.5% 35234.77 vpx/crypto/tcrypt/2s-205-210
> 2711.31 +973.8% 29114.07 vpx/crypto/tcrypt/2s-301-319
> 2369.23 +940.3% 24648.12 vpx/crypto/tcrypt/2s-401-417
> 2620.64 +1428.7% 40060.71 vpx/crypto/tcrypt/2s-500-504
> 1713.98 +1624.3% 29553.72 vpx/crypto/tcrypt/2s-505-509
> 3423353.12 +1184.9% 43985148.08 TOTAL lock_stat.vmap_area_lock.holdtime-total
>
> The format of report is
>
> parent commit commit
> ------------------------ ------------------------
> number %change number testbox/testcase/test-params
> ...
> ...
> ...
> total number %change total number TOTAL perf-metric-name being compared

That's a lot of slowdowns, especially for such a simple patch.

Peter, any ideas?



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