Messages in this thread | | | Date | Mon, 19 Apr 2021 21:17:12 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH] smp: add a best_effort version of smp_call_function_many() |
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On Mon, Apr 19, 2021 at 11:44:55AM -0700, Luigi Rizzo wrote: > Regardless of the 'wait' argument, smp_call_function_many() must spin > if any of the target CPUs have their csd busy waiting to be processed > for a previous call. This may cause high tail latencies e.g. when some > of the target CPUs are running functions that disable interrupts for a > long time; getrusage() is one possible culprit. > > Here we introduce a variant, __smp_call_function_many(), that adds > a third 'best_effort' mode to the two existing ones (nowait, wait). > In best effort mode, the call will skip CPUs whose csd is busy, and if > any CPU is skipped it returns -EBUSY and the set of busy in the mask. > This allows the caller to decide how to proceed, e.g. it might retry at > a later time, or use a private csd, etc.. > > The new function is a compromise to avoid touching existing callers of > smp_call_function_many(). If the feature is considered interesting, we > could even replace the 'wait' argument with a ternary 'mode' in all > smp_call_function_*() and derived methods.
I don't see a user of this...
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