On Mon, Oct 21, 2019 at 09:59:42AM +0200, Ingo Molnar wrote: > > * Alexey Budankov <alexey.budan...@linux.intel.com> wrote: > > > + /* > > + * PMU specific parts of task perf context may require > > + * additional synchronization, at least for proper Intel > > + * LBR callstack data profiling; > > + */ > > + pmu->sync_task_ctx(ctx->task_ctx_data, > > + next_ctx->task_ctx_data); > > Firstly, I'm pretty sure you never run this on a CPU where > pmu->sync_task_ctx is NULL, right? ;-) > > Secondly, even on Intel CPUs in many cases we'll just call into a ~2 deep > function pointer based call hierarchy, just to find that nothing needs to
See prototype here for getting rid of at least one layer of indirect calls: https://lkml.kernel.org/r/20191007083831.2688070...@infradead.org > be done, because there's no LBR call stack maintained: > > + if (!one || !another) > + return; > > So while it's technically a layering violation, it might make sense to > elevate this check to the generic layer and say that synchronization > calls by the core layer will always provide two valid pointers? Alternatively we can write the thing like: if (pmu->swap_task_ctx) pmu->swap_task_ctx(ctx, next_ctx) else swap(ctx->task_ctx_data, next_ctx->task_ctx_data);
