From: Peter Hurley <peter@hurleysoftware.com>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
LKML <linux-kernel@vger.kernel.org>,
lkp@01.org, Tejun Heo <tj@kernel.org>
Subject: Re: increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data"
Date: Tue, 17 Sep 2013 20:49:51 -0400 [thread overview]
Message-ID: <5238F8AF.4050309@hurleysoftware.com> (raw)
In-Reply-To: <20130913010936.GA1291@localhost>
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 [*].
[...]
> 8cb06c983822103da1cf 20bafb3d23d108bc0a89
> ------------------------ ------------------------
> 976.67 +108.3% 2034.67 lkp-a04/micro/netperf/120s-200%-TCP_STREAM
> 8971.36 +11.4% 9997.05 nhm-white/micro/aim7/exec_test
> 9948.03 +20.9% 12031.72 TOTAL slabinfo.kmalloc-128.active_objs
>
> 8cb06c983822103da1cf 20bafb3d23d108bc0a89
> ------------------------ ------------------------
> 976.67 +108.3% 2034.67 lkp-a04/micro/netperf/120s-200%-TCP_STREAM
> 9127.64 +11.4% 10164.15 nhm-white/micro/aim7/exec_test
> 10104.31 +20.7% 12198.82 TOTAL slabinfo.kmalloc-128.num_objs
The dramatic increase in 128-byte kmalloc blocks is from vmalloc overhead
with associated with each allocation. On a x86_64, struct vmap_area is 104 bytes,
rounded to 128, allocated with every vmalloc allocation. This is approx 1% overhead
(which seems high to me).
The reason this is still visible after the test completes is the vmap area is
lazily reclaimed (see mm/vmalloc.c:__purge_vmap_area_lazy()).
1% memory overhead coupled with the unwanted vmap_area_lock contention (even though it is
test-induced) -- I might revert this anyway.
Regards,
Peter Hurley
next prev parent reply other threads:[~2013-09-18 0:49 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-13 0:51 increased vmap_area_lock contentions on "n_tty: Move buffers into n_tty_data" Fengguang Wu
2013-09-13 1:09 ` Fengguang Wu
2013-09-17 15:34 ` Peter Hurley
2013-09-17 23:22 ` Fengguang Wu
2013-09-18 0:22 ` Peter Hurley
2013-09-25 9:04 ` Lin Ming
2013-09-25 11:30 ` Peter Hurley
2013-09-25 14:53 ` Lin Ming
2013-09-25 16:02 ` Lin Ming
2013-09-26 3:20 ` Andi Kleen
2013-09-26 11:52 ` Peter Hurley
2013-09-26 15:32 ` Andi Kleen
2013-09-26 17:22 ` Peter Hurley
2013-09-26 7:33 ` Andrew Morton
2013-09-26 11:31 ` Peter Hurley
2013-09-26 15:04 ` Greg KH
2013-09-26 17:35 ` Peter Hurley
2013-09-26 18:05 ` Andrew Morton
2013-09-26 21:42 ` Peter Hurley
2013-09-26 21:58 ` Andrew Morton
2013-09-26 22:21 ` Peter Hurley
2013-09-18 0:49 ` Peter Hurley [this message]
2013-09-13 3:17 ` Greg KH
2013-09-13 3:38 ` Fengguang Wu
2013-09-13 3:44 ` Greg KH
2013-09-13 9:55 ` Peter Hurley
2013-09-13 12:34 ` Greg KH
2013-09-17 2:42 ` Peter Hurley
2013-09-17 2:56 ` Fengguang Wu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=5238F8AF.4050309@hurleysoftware.com \
--to=peter@hurleysoftware.com \
--cc=fengguang.wu@intel.com \
--cc=gregkh@linuxfoundation.org \
--cc=linux-kernel@vger.kernel.org \
--cc=lkp@01.org \
--cc=tj@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox