Messages in this thread | | | From | Nadav Amit <> | Subject | Re: [PATCH v5 1/8] smp: Run functions concurrently in smp_call_function_many_cond() | Date | Tue, 16 Feb 2021 18:53:09 +0000 |
| |
> On Feb 16, 2021, at 8:32 AM, Peter Zijlstra <peterz@infradead.org> wrote: > > On Tue, Feb 09, 2021 at 02:16:46PM -0800, Nadav Amit wrote: >> From: Nadav Amit <namit@vmware.com> >> >> Currently, on_each_cpu() and similar functions do not exploit the >> potential of concurrency: the function is first executed remotely and >> only then it is executed locally. Functions such as TLB flush can take >> considerable time, so this provides an opportunity for performance >> optimization. >> >> To do so, modify smp_call_function_many_cond(), to allows the callers to >> provide a function that should be executed (remotely/locally), and run >> them concurrently. Keep other smp_call_function_many() semantic as it is >> today for backward compatibility: the called function is not executed in >> this case locally. >> >> smp_call_function_many_cond() does not use the optimized version for a >> single remote target that smp_call_function_single() implements. For >> synchronous function call, smp_call_function_single() keeps a >> call_single_data (which is used for synchronization) on the stack. >> Interestingly, it seems that not using this optimization provides >> greater performance improvements (greater speedup with a single remote >> target than with multiple ones). Presumably, holding data structures >> that are intended for synchronization on the stack can introduce >> overheads due to TLB misses and false-sharing when the stack is used for >> other purposes. >> >> Reviewed-by: Dave Hansen <dave.hansen@linux.intel.com> >> Cc: Peter Zijlstra <peterz@infradead.org> >> Cc: Rik van Riel <riel@surriel.com> >> Cc: Thomas Gleixner <tglx@linutronix.de> >> Cc: Andy Lutomirski <luto@kernel.org> >> Cc: Josh Poimboeuf <jpoimboe@redhat.com> >> Signed-off-by: Nadav Amit <namit@vmware.com> > > Kernel-CI is giving me a regression that's most likely this patch: > > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F%2Fkernelci.org%2Ftest%2Fcase%2Fid%2F602bdd621c979f83faaddcc6%2F&data=04%7C01%7Cnamit%40vmware.com%7C7dc93f3b74d8488de06f08d8d2988b0a%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7C637490899907612612%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&sdata=PFs0ydMLh6xVfAQzAxSNd108YjxKMopNwxqsm82lEog%3D&reserved=0 > > I'm not sure I can explain it yet. It did get me looking at > on_each_cpu() and it appears that wants to be converted too, something > like the below perhaps.
Looks like a good cleanup, but I cannot say I understand the problem and how it would solve it. Err...
| |