Re: [PATCH] powerpc: mitigate impact of decrementer reset
From: Michael Ellerman <mpe@ellerman.id.au>
Date: 2014-11-18 01:46:57
On Mon, 2014-11-17 at 11:18 -0800, Paul E. McKenney wrote:
On Thu, Nov 13, 2014 at 01:42:12PM +1100, Michael Ellerman wrote:quoted
On Mon, 2014-11-10 at 14:58 -0600, Paul Clarke wrote:quoted
On 11/10/2014 04:08 AM, Benjamin Herrenschmidt wrote:quoted
On Tue, 2014-10-07 at 14:13 -0500, Paul Clarke wrote:quoted
This patch short-circuits the reset of the decrementer, exiting after the decrementer reset, but before the housekeeping tasks if the only need for the interrupt is simply to reset it. After this patch, the latency spike was measured at about 150 nanoseconds.Doesn't this break the irq_work stuff ? We trigger it with a set_dec(1); and your patch will probably cause it to be skipped...You're right.Yeah, thanks Ben, that would have been bad. So we'll need to come up with a different approach.If I am understanding this correctly, it underscores the need for more bits in the decrementer register. :-/
Yes that is the root cause of the problem :) cheers