On 3/18/19 7:10 PM, Linus Torvalds wrote:
On Mon, Mar 18, 2019 at 10:51 AM Peter Zijlstra <pet...@infradead.org> wrote:
How about I do a patch that schedules EFLAGS for both 32bit and 64bit,
mark this for backporting to infinity.
And then at the end, after the objtool-ac bits land, I do a patch
removing the EFLAGS scheduling for x86_64.
Sounds sane to me.
And we can make it AC-conditional if it's actually shown to be visible
from a performance standpoint.
But iirc pushf/popf isn't really that expensive - in fact I think it's
pretty cheap when system flags don't change.
I did not see evidence of this. In my testing,
POPF is always ~20 cycles, even if popped flags are identical to current
state of flags.
