From: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: John Stultz <john.stultz@linaro.org>,
Stephen Boyd <sboyd@kernel.org>,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] timer: Use static_branch_likely() for timers_nohz_active
Date: Wed, 23 Jun 2021 11:17:01 +0800 [thread overview]
Message-ID: <20210623111701.0850fac3@xhacker.debian> (raw)
In-Reply-To: <87o8bydj0n.ffs@nanos.tec.linutronix.de>
Hi Thomas,
On Tue, 22 Jun 2021 17:19:20 +0200
Thomas Gleixner <tglx@linutronix.de> wrote:
>
> On Thu, May 13 2021 at 14:33, Jisheng Zhang wrote:
> > NOHZ is likely to be enabled, so use static_branch_likely() to
>
> Why is it likely to be enabled? Did you make a survey of the wider
> distro universe or what?
No, I didn't make any survey. I only checked debian and ubuntu kernel
image config file, both have CONFIG_NO_HZ_COMMON=y
So IMHO, if CONFIG_NO_HZ_COMMON=y, the static key timers_nohz_active is
true in most cases.
>
> > reflect this fact. This could improve the finally generated code
>
> could improve? Either it does or it does not.
Per include/linux/jump_label.h, if the timers_nohz_active is true,
it can save two jmp instructions.
* type\branch| likely (1) | unlikely (0)
* -----------+-----------------------+------------------
* | |
* true (1) | ... | ...
* | NOP | JMP L
* | <br-stmts> | 1: ...
* | L: ... |
* | |
* | | L: <br-stmts>
* | | jmp 1b
Thanks
next prev parent reply other threads:[~2021-06-23 3:17 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-13 6:33 [PATCH] timer: Use static_branch_likely() for timers_nohz_active Jisheng Zhang
2021-06-22 15:19 ` Thomas Gleixner
2021-06-23 3:17 ` Jisheng Zhang [this message]
2021-06-23 10:41 ` Jisheng Zhang
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