From: Valentin Schneider <valentin.schneider@arm.com>
To: Alexey Dobriyan <adobriyan@gmail.com>,
mingo@redhat.com, peterz@infradead.org
Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
linux-block@vger.kernel.org, dm-devel@redhat.com,
axboe@kernel.dk, aarcange@redhat.com
Subject: Re: [PATCH] sched: make struct task_struct::state 32-bit
Date: Tue, 3 Sep 2019 00:02:38 +0100 [thread overview]
Message-ID: <7b94004e-4a65-462b-cd6b-5cbd23d607bf@arm.com> (raw)
In-Reply-To: <20190902210558.GA23013@avx2>
Hi,
On 02/09/2019 22:05, Alexey Dobriyan wrote:
> 32-bit accesses are shorter than 64-bit accesses on x86_64.
> Nothing uses 64-bitness of ->state.
>
> Space savings are ~2KB on F30 kernel config.
>
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
Interestingly this has been volatile long since forever (or 2002, which is
my take on "forever" given the history tree), although the task states
seem to have never gone above 0x1000 (the current TASK_STATE_MAX).
[...]
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -643,7 +643,7 @@ struct task_struct {
> struct thread_info thread_info;
> #endif
> /* -1 unrunnable, 0 runnable, >0 stopped: */
> - volatile long state;
> + volatile int state;
This leads to having some padding after this field (w/o randomization):
struct task_struct {
struct thread_info thread_info; /* 0 24 */
volatile int state; /* 24 4 */
/* XXX 4 bytes hole, try to pack */
void * stack; /* 32 8 */
Though seeing as this is also the boundary of the randomized layout we can't
really do much better without changing the boundary itself. So much for
cacheline use :/
Anyway, task_struct doesn't shrink but we can cut some corners in the asm,
I guess that's fine?
[...]
next prev parent reply other threads:[~2019-09-02 23:02 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-09-02 21:05 [PATCH] sched: make struct task_struct::state 32-bit Alexey Dobriyan
2019-09-02 23:02 ` Valentin Schneider [this message]
2019-09-03 16:23 ` Alexey Dobriyan
2019-09-03 16:31 ` Valentin Schneider
2019-09-03 6:51 ` [dm-devel] " Christoph Hellwig
2019-09-03 7:13 ` Peter Zijlstra
2019-09-03 17:29 ` Valentin Schneider
2019-09-03 18:19 ` Alexey Dobriyan
2019-09-03 21:51 ` Valentin Schneider
2019-09-04 12:07 ` Valentin Schneider
2019-09-04 17:48 ` Valentin Schneider
2019-09-05 15:51 ` Markus Elfring
2019-09-05 16:52 ` Valentin Schneider
2019-09-23 10:26 ` Valentin Schneider
2019-09-23 10:34 ` Julia Lawall
2019-09-23 11:26 ` Valentin Schneider
2019-09-23 11:43 ` Julia Lawall
2019-09-23 13:23 ` Valentin Schneider
2019-09-24 8:28 ` Markus Elfring
2019-09-24 8:07 ` Markus Elfring
2019-09-04 9:43 ` [PATCH] " David Laight
2019-09-04 10:25 ` Valentin Schneider
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