From: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Sent: Sunday, October 27, 2019 8:20 AM > > When sending an IPI to a single CPU there is no need to deal with cpumasks. > With 2 CPU guest on WS2019 I'm seeing a minor (like 3%, 8043 -> 7761 CPU > cycles) improvement with smp_call_function_single() loop benchmark. The > optimization, however, is tiny and straitforward. Also, send_ipi_one() is > important for PV spinlock kick. > > I was also wondering if it would make sense to switch to using regular > APIC IPI send for CPU > 64 case but no, it is twice as expesive (12650 CPU > cycles for __send_ipi_mask_ex() call, 26000 for orig_apic.send_IPI(cpu, > vector)). > > Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > --- > Changes since v2: > - Check VP number instead of CPU number against >= 64 [Michael] > - Check for VP_INVAL > Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
