Messages in this thread | | | Date | Mon, 23 May 2011 17:27:17 +0200 | Subject | Re: [PATCH 0/3] perf_events: update extra shared registers management (v2) | From | Stephane Eranian <> |
| |
On Mon, May 23, 2011 at 5:15 PM, Peter Zijlstra <peterz@infradead.org> wrote: > On Mon, 2011-05-23 at 14:00 +0200, Stephane Eranian wrote: >> On Mon, May 23, 2011 at 1:10 PM, Peter Zijlstra <peterz@infradead.org> wrote: >> > On Mon, 2011-05-23 at 12:58 +0200, Stephane Eranian wrote: >> >> There is a major issue as it stands, though. You can >> >> get into an infinite loop bouncing between RSP_0 and RSP_1 >> >> in case there is no solution in the group, i.e., you have 3 values >> >> for the extra MSR. I think you need to count the number of times >> >> you've called intel_try_alt_er() with success or maintain some sort >> >> of bitmask of possible alternate choices and when you exhaust that, >> >> you simply fail. >> > >> > That should be sorted by the compare with the initial idx value, no? >> > Once its back where it started out it'll bail. >> > >> Nope. >> >> Take: >> - ev1=rsp_0:0x1001 >> - ev2=rsp_0:0x1002 >> - ev3=rsp_1:0x1008 >> >> ev1-> rsp_0 >> ev2-> rsp_0, conflict, then try yields rsp_1 -> ok >> ev3 -> rsp_1, conflict, then rsp_0, but fails, try again -> rsp_1, >> fails, and so on >> >> The issue is that the intel_try() function does not know the >> history of the swaps between rsp_0, rsp1. > > But it does, we pass the initial reg->idx in, and return false when that > matches the new idx, so in your example, ev3 will do: > > rsp_1 -> conflict, > try rsp_0 -> conflict, > try rsp_1 -> bail, return emptyconstraint > > Ok, my fault. That's because I tweaked your patch a bit and I did not keep track of idx. I guess the logic is not obvious. I think you should rename idx to orig_idx.
> -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |