> On Sep 10, 2021, at 11:58 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > On Fri, Sep 10, 2021 at 11:33:52AM -0700, Song Liu wrote: >> + /* Given we stop LBR in software, we will waste a few entries. >> + * But we should try to waste as few as possible entries. We are at >> + * about 7 on x86_64 systems. >> + * Add a check for < 10 so that we get heads-up when something >> + * changes and wastes too many entries. >> + */ >> + ASSERT_LT(skel->bss->wasted_entries, 10, "check_wasted_entries"); > > It might be worth pointing out that you can easily bust this limit by > enabling all the various tracepoints that are still in that code, but > that that isn't a hard error since that's not the expected use case. > > For example there's the wrmsr tracepoint that will inject 6 or so > branches on top of that you now have. And I also think there's a > tracepoint in local_irq_save() that can trigger. Right. I did some test with a lot of debug config enabled. We do see a lot more wasted entries there. Thanks, Song
