linux-kernel - Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty

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Message-ID: <20130913034413.GA26166@kroah.com>
Date:	Thu, 12 Sep 2013 20:44:13 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	Fengguang Wu <fengguang.wu@...el.com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	LKML <linux-kernel@...r.kernel.org>, lkp@...org,
	Tejun Heo <tj@...nel.org>
Subject: Re: 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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