On 06/17/2014 05:18 PM, Paul E. McKenney wrote: > So if I understand correctly, a goodly part of the regression is due not > to the overhead added to cond_resched(), but rather because grace periods > are now happening faster, thus incurring more overhead. Is that correct?
Yes, that's the theory at least. > If this is the case, could you please let me know roughly how sensitive is > the performance to the time delay in RCU_COND_RESCHED_EVERY_THIS_JIFFIES? This is the previous kernel, plus RCU tracing, so it's not 100% apples-to-apples (and it peaks a bit lower than the other kernel). But here's the will-it-scale open1 throughput on the y axis vs RCU_COND_RESCHED_EVERY_THIS_JIFFIES on x: http://sr71.net/~dave/intel/jiffies-vs-openops.png This was a quick and dirty single run with very little averaging, so I expect there to be a good amount of noise. I ran it from 1->100, but it seemed to peak at about 30. > The patch looks promising. I will probably drive the time-setup deeper > into the guts of RCU, which should allow moving the access to jiffies > and the comparison off of the fast path as well, but this appears to > me to be good and sufficient for others encountering this same problem > in the meantime. Yeah, the more overhead we can push out of cond_resched(), the better. I had no idea how much we call it! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/