From: Ingo Molnar <mingo@kernel.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
"Frédéric Weisbecker" <fweisbec@gmail.com>,
"Thomas Gleixner" <tglx@linutronix.de>,
"Peter Zijlstra" <a.p.zijlstra@chello.nl>,
"Andrew Morton" <akpm@linux-foundation.org>
Subject: Re: [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to 'unsigned int'
Date: Tue, 15 Mar 2016 13:15:25 +0100 [thread overview]
Message-ID: <20160315121525.GA3991@gmail.com> (raw)
In-Reply-To: <20160315095337.GC7943@gmail.com>
* Ingo Molnar <mingo@kernel.org> wrote:
>
> Linus noticed that the new tick_dep_mask types introduced in:
>
> d027d45d8a17 ("nohz: New tick dependency mask")
>
> ... are sloppily defined as 'unsigned long' - which is wasteful
> to carry just 4 bits and which may also create suboptimal data
> types on 64-bit systems with word alignment padding holes in them.
>
> Fix this by changing the type to the more natural 'unsigned int'.
>
> (The xchg_or() API will work fine with 'unsigned int' as well.)
>
> Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
> Cc: Chris Metcalf <cmetcalf@ezchip.com>
> Cc: Frederic Weisbecker <fweisbec@gmail.com>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: Chris Metcalf <cmetcalf@ezchip.com>
> Cc: Ingo Molnar <mingo@kernel.org>
> Cc: Luiz Capitulino <lcapitulino@redhat.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Rik van Riel <riel@redhat.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Viresh Kumar <viresh.kumar@linaro.org>
> Signed-off-by: Ingo Molnar <mingo@kernel.org>
> ---
> include/linux/sched.h | 4 ++--
> kernel/time/tick-sched.c | 11 +++++------
> 2 files changed, 7 insertions(+), 8 deletions(-)
Hm, so the problem I did not consider is the following:
triton:~/tip> git grep tick_dep_mask kernel | grep _bit
kernel/time/tick-sched.c: clear_bit(bit, &tick_dep_mask);
kernel/time/tick-sched.c: clear_bit(bit, &ts->tick_dep_mask);
kernel/time/tick-sched.c: clear_bit(bit, &tsk->tick_dep_mask);
kernel/time/tick-sched.c: clear_bit(bit, &sig->tick_dep_mask);
and the bitops natural type (and in fact the only supported bitops type) is
'unsigned long'.
So it's not that easy to change a bitmask over to unsigned int.
Suggestions?
Thanks,
Ingo
next prev parent reply other threads:[~2016-03-15 12:15 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-14 12:32 [GIT PULL] NOHZ updates for v4.6 Ingo Molnar
2016-03-15 2:44 ` Linus Torvalds
2016-03-15 8:42 ` Peter Zijlstra
2016-03-15 9:49 ` Ingo Molnar
2016-03-15 9:32 ` [PATCH] atomic: Fix bugs in 'fetch_or()' and rename it to 'xchg_or()' Ingo Molnar
2016-03-15 10:50 ` Peter Zijlstra
2016-03-15 12:08 ` Ingo Molnar
2016-03-15 12:42 ` Peter Zijlstra
2016-03-15 11:06 ` Peter Zijlstra
2016-03-15 11:59 ` Peter Zijlstra
2016-03-15 12:01 ` Ingo Molnar
2016-03-15 12:32 ` Ingo Molnar
2016-03-15 12:37 ` Ingo Molnar
2016-03-15 13:17 ` Peter Zijlstra
2016-03-15 12:21 ` [PATCH v2] " Ingo Molnar
2016-03-15 13:26 ` Peter Zijlstra
2016-03-16 8:04 ` Ingo Molnar
2016-03-16 8:29 ` Peter Zijlstra
2016-03-15 17:08 ` Frederic Weisbecker
2016-03-16 8:14 ` Ingo Molnar
2016-03-17 0:54 ` Frederic Weisbecker
2016-03-15 16:18 ` [PATCH] " Linus Torvalds
2016-03-15 9:53 ` [PATCH] nohz: Change tick_dep_mask from 'unsigned long' to 'unsigned int' Ingo Molnar
2016-03-15 12:15 ` Ingo Molnar [this message]
2016-03-15 16:30 ` Linus Torvalds
2016-03-15 17:28 ` Frederic Weisbecker
2016-03-15 17:36 ` Linus Torvalds
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