On Sat, May 15, 2010 at 04:59:52PM -0600, Grant Grundler wrote: > On Sat, May 15, 2010 at 01:27:49PM -0400, Kyle McMartin wrote: > > It's a two instruction penalty(*) in the kernel syscall return path, just > > do it there. I've got a box at Red Hat with all the source to the whole > > damn world on it we run greps against to look for dumb stuff like memcpy > > bugs. > > Why look for it? Just change the kernel to not ever return one of them. > Because the failure case of just changing the #define in the kernel is a runtime error for old code. > > I'll toss a grep for EAGAIN and not EWOULDBLOCK and vice versa and > > see how much stuff might b0rk. > > Please do...I'd be curious to see which programs might be affected and > if we care. > > > We discussed this a couple years ago, and it ended up being a complete > > rats nest of error returns that needed fixing. > > > > regards, Kyle. > > > > *: CMPI,N(=), LDI, maybe a third since I don't remember how sign > > extension works off the top of my head. > > Mispredicted branches cost something like 20-25 cycles. I forgot now but I > do know they aren't cheap. > That's not a branch, Grant. > I'd rather not add more hacks for this they are unlikely to ever > be removed again. I'd rather have status quo than add some hack > to the syscall return path. > The alternative is to rebuild all of userspace, again. regards, Kyle -- To unsubscribe from this list: send the line "unsubscribe linux-parisc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
