On Mon, 2017-11-13 at 21:25 +0100, Thomas Gleixner wrote: > On Mon, 13 Nov 2017, Dey, Megha wrote: > > >-----Original Message----- > > >From: Peter Zijlstra [mailto:peterz@xxxxxxxxxxxxx] > > >Sent: Monday, November 13, 2017 1:00 AM > > >To: Megha Dey <megha.dey@xxxxxxxxxxxxxxx> > > >Cc: x86@xxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; linux- > > Please fix your mail client so it does not add this complete useless > information to the reply. Will fix this. > > > >On Sat, Nov 11, 2017 at 01:20:05PM -0800, Megha Dey wrote: > > >> +/* > > >> + * Unmask the NMI bit of the local APIC the first time task is > > >> +scheduled > > >> + * on a particular CPU. > > >> + */ > > >> +static void intel_bm_unmask_nmi(void) { > > >> + this_cpu_write(bm_unmask_apic, 0); > > >> + > > >> + if (!(this_cpu_read(bm_unmask_apic))) { > > >> + apic_write(APIC_LVTPC, APIC_DM_NMI); > > >> + this_cpu_inc(bm_unmask_apic); > > >> + } > > >> +} > > > > > >What? Why? > > > > > Normally, other drivers using perf create an event on every CPU (thereby > > calling perf_init on every CPU), where this bit(APIC_DM_NMI)is explicitly > > unmasked. In our driver, we do not do this (since we are worried only > > about a particular task) and hence this bit is only disabled on the local > > APIC where the perf event is initialized. > > > > As such, if the task is scheduled out to some other CPU, this bit is set > > and hence would stop the interrupt from reaching the processing core. > > Still that code makes no sense at all and certainly does not do what you > claim it does: > > > >> + this_cpu_write(bm_unmask_apic, 0); > > >> + > > >> + if (!(this_cpu_read(bm_unmask_apic))) { > > So first you write the per cpu variable to 0 and then you check whether it > is zero, which is pointless obviously. yes, I see your point. The logic is flawed. Will fix this. > > > > > > >> +static int intel_bm_event_add(struct perf_event *event, int mode) { > > Please move the opening bracket of the function into the next line. See the > kernel coding style documentation. Will do. > > Thanks, > > tglx -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
