linux-kernel - Re: [PATCH] Reduce overhead of CONFIG_TIMER

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20071217090337.0b1af816@laptopd505.fenrus.org>
Date:	Mon, 17 Dec 2007 09:03:37 -0800
From:	Arjan van de Ven <arjan@...radead.org>
To:	Arnaldo Carvalho de Melo <acme@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH] Reduce overhead of CONFIG_TIMER_STATS

On Sun, 16 Dec 2007 19:29:44 -0200
Arnaldo Carvalho de Melo <acme@...hat.com> wrote:

> Hi,
> 	While looking at the pahole output for struct timer_list on
> recent kernels I noticed that there is a 4 bytes padding on struct
> timer_list that gets propagated to many structs on 64 bits
> architectures:
> 
> [acme@...pio linux-2.6]$ pahole -C timer_list /tmp/tcp.o.before
> struct timer_list {
>         struct list_head      entry;          /*     0    16 */
>         long unsigned int     expires;        /*    16     8 */
>         void                  (*function)(long unsigned int); /*
> 24     8 */ long unsigned int     data;           /*    32     8 */
>         struct tvec_t_base_s *base;           /*    40     8 */
>         void *                start_site;     /*    48     8 */
>         char                  start_comm[16]; /*    56    16 */
>         /* --- cacheline 1 boundary (64 bytes) was 8 bytes ago --- */
>         int                   start_pid;      /*    72     4 */
> 
>         /* size: 80, cachelines: 2 */
>         /* padding: 4 */
>         /* last cacheline: 16 bytes */
> };
> [acme@...pio linux-2.6]$
> 
> 	So the attached patch reduces the 4 bytes hole overhead of
> CONFIG_TIMER_STATS on 64bit architectures by shrinking the field for
> the process name by 4 bytes.
> 
> 	Statistically this doesn't affects that many process names as
> most are less than 12 bytes. As CONFIG_TIMER_STATS is enabled at least
> on fedora kernels I think that we can, with this patch, still reap the
> benefits of powertopping.

I'm still worried that this means that PowerTOP will end up displaying shortened names..
it's already sometimes tricky to know who's guilty at 16... at 12 I fear it just gets worse.
Isn't there some other reorder that you can do to still get rid of the hole?


-- 
If you want to reach me at my work email, use arjan@...ux.intel.com
For development, discussion and tips for power savings, 
visit http://www.lesswatts.org
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/