Messages in this thread | | | Date | Wed, 23 Jun 2021 11:17:01 +0800 | From | Jisheng Zhang <> | Subject | Re: [PATCH] timer: Use static_branch_likely() for timers_nohz_active |
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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
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