Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data"

[Fengguang Wu <fengguang.wu@intel.com>]

On Tue, Sep 17, 2013 at 11:34:21AM -0400, Peter Hurley wrote:
> On 09/12/2013 09:09 PM, Fengguang Wu 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:
> >>
> >>commit 20bafb3d23d108bc0a896eb8b7c1501f4f649b77
> >>Author: Peter Hurley <peter@hurleysoftware.com>
> >>Date:   Sat Jun 15 10:21:19 2013 -0400
> >>
> >>     n_tty: Move buffers into n_tty_data
> >>
> >>     Reduce pointer reloading and improve locality-of-reference;
> >>     allocate read_buf and echo_buf within struct n_tty_data.
> >
> >Here are some comparison between this commit [o] with its parent commit [*].
> 
> Hi Fenguang,
> 
> Can you give the particulars of the aim7 test runs below?
> I ask because I get _no_ added contention on the vmap_area_lock when I run
> these tests on a dual-socket xeon.
> 
> What is the machine configuration(s)?
> Are you using the aim7 'multitask' test driver or your own custom driver?
> What is the load configuration (ie., constant, linearly increasing, convergence)?
> How many loads are you simulating?

The aim7 tests are basically

        (       
                echo $HOSTNAME
                echo $workfile
                
                echo 1
                echo 2000
                echo 2
                echo 2000
                echo 1
        ) | ./multitask -t

>                        lock_stat.vmap_area_lock.holdtime-total
> [...]
> >                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
> [...]
> >                822461.02     +1585.0%  13858430.62  nhm-white/micro/aim7/exec_test
> >                  9858.11     +2715.9%    277595.41  nhm-white/micro/aim7/fork_test
> [...]
> >                   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
> 
> 
> None of the tests below execute a code path that leads to get_vmalloc_info().
> The only in-kernel user of get_vmalloc_info() is a sysfs read of /proc/meminfo,
> which none of the tests below perform.
> 
> What is reading /proc/meminfo?

Good point! That may explain it:  I'm running a

loop:
        cat /proc/meminfo
        sleep 1
 
in all the tests.

Thanks,
Fengguang

> >                  lock_stat.vmap_area_lock.contentions.get_vmalloc_info
> >
> >     8cb06c983822103da1cf      20bafb3d23d108bc0a89
> >------------------------  ------------------------
> >                  4952.40      +447.0%     27090.40  lkp-ne04/micro/aim7/shell_rtns_1
> >                 28410.80      +556.2%    186423.00  lkp-snb01/micro/aim7/exec_test
> >                  8142.00      +615.4%     58247.33  nhm-white/micro/aim7/exec_test
> >                  1386.00      +762.6%     11955.20  nhm-white/micro/aim7/shell_rtns_1
> >                 42891.20      +561.5%    283715.93  TOTAL lock_stat.vmap_area_lock.contentions.get_vmalloc_info