On Mon, Jun 29, 2015 at 12:28:32PM +0200, Christoffer Dall wrote: > On Thu, Jun 25, 2015 at 06:12:18PM +0200, Andrew Jones wrote: > > spinlock torture tests made it clear that checking mmu_enabled() > > every time we call spin_lock is a bad idea. > > why a bad idea? Does it break, is it slow? Just slow, but really slow. After porting vos' spinlock test over, there were three implementations to compare, this one, gcc-builtin, and none. none doesn't really matter as it's not "real". gcc-builtin took about 6 seconds to complete on my machine (an x86 notebook, recall it's a tcg test), and this one took 20 seconds. > > > As most tests will > > want the MMU enabled the entire time, then just hard code > > mmu_enabled() to true. Tests that want to play with the MMU can > > be compiled with CONFIG_MAY_DISABLE_MMU to get the actual check > > back. > > If we don't care about performance, why this added complexity? I think the series I sent that allows us to optimize mmu_enabled() has about the same level of complexity, not much, but now we also only take 6 seconds with the test. So, IMO, the extra _count variable is worth it. Thanks, drew -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
