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While staring at build_sched_domains(), I realized that get_group() does several duplicate (thus useless) writes. If you take the Arm Juno r0 (LITTLEs = [0, 3, 4, 5], bigs = [1, 2]), the sched_group build flow would look like this: ('MC[cpu]->sg' means 'per_cpu_ptr(&tl->data->sg, cpu)' with 'tl == MC') build_sched_groups(MC[CPU0]->sd, CPU0) get_group(0) -> MC[CPU0]->sg get_group(3) -> MC[CPU3]->sg get_group(4) -> MC[CPU4]->sg get_group(5) -> MC[CPU5]->sg build_sched_groups(DIE[CPU0]->sd, CPU0) get_group(0) -> DIE[CPU0]->sg get_group(1) -> DIE[CPU1]->sg <=================+ | build_sched_groups(MC[CPU1]->sd, CPU1) | get_group(1) -> MC[CPU1]->sg | get_group(2) -> MC[CPU2]->sg | | build_sched_groups(DIE[CPU1]->sd, CPU1) ^ get_group(1) -> DIE[CPU1]->sg } We've set up these two up here! get_group(3) -> DIE[CPU0]->sg } From this point on, we will only use sched_groups that have been previously visited & initialized. The only new operation will be which group pointer we affect to sd->groups. On the Juno r0 we get 32 get_group() calls, every single one of them writing to a sched_group->cpumask. However, all of the data structures we need are set up after 8 visits (see above). Return early from get_group() if we've already visited (and thus initialized) the sched_group we're looking at. Overlapping domains are not affected as they do not use build_sched_groups(). Tested on a Juno and a 2 * (Xeon E5-2690) system. ( FWIW I initially checked the refs for both sg && sg->sgc, but figured if they weren't both 0 or > 1 then something must have gone wrong, so I threw in a WARN_ON(). ) No change in functionality intended. Signed-off-by: Valentin Schneider <valentin.schneider@arm.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar <mingo@kernel.org> |
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crypto | ||
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drivers | ||
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kernel | ||
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usr | ||
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README |
Linux kernel ============ There are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. Please read Documentation/admin-guide/README.rst first. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. The formatted documentation can also be read online at: https://www.kernel.org/doc/html/latest/ There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.