* Juergen Gross <[email protected]> wrote:
> On 21/06/18 16:02, Ingo Molnar wrote: > > > > * Ingo Molnar <[email protected]> wrote: > > > >> > >> * Mikulas Patocka <[email protected]> wrote: > >> > >>> The sleeping functions down, down_interruptible, down_killable and > >>> down_timeout can't be called with interrupts disabled, so we don't have to > >>> save and restore interrupt flag. > >>> > >>> This patch avoids the costly pushf and popf instructions on the semaphore > >>> path. > >>> > >>> Signed-off-by: Mikulas Patocka <[email protected]> > >>> > >>> --- > >>> kernel/locking/semaphore.c | 21 ++++++++------------- > >>> 1 file changed, 8 insertions(+), 13 deletions(-) > >> > >> I've applied this to the locking tree, I suspect we can do this on the > >> condition > >> that it doesn't explode in early boot code (which has irqs disabled) and > >> doesn't > >> generate early boot lockdep splats either. > > > > Hm, this blew up pretty quick on a pretty regular x86-64 PC white-box, > > during > > early bootup: > > > > PANIC: early exception 0x08 IP 246:10 error ffffffff811537b2 cr2 > > 0xffff88000240cff8 > > > > and I think it's due to your patch - verifying that now. > > I guess local_irq_enable() being called by raw_spin_unlock_irq() makes > its usage in early boot code undesirable. > > Maybe it would be possible to use alternatives for that case? They are > applied after enabling interrupts, so pushf and popf instructions could > be patched away. Or we could just leave the code as-is: the performance difference between CLI/STI and PUSHF/POPF shouldn't be significant, plus the semaphore APIs are obsolete and should not be used. Thanks, Ingo
