On Fri, Aug 30, 2013 at 5:34 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > On Fri, Aug 30, 2013 at 2:27 AM, Sedat Dilek <sedat.dilek@xxxxxxxxx> wrote: >> >> Here on Ubuntu/precise v12.04.3 AMD64 I get these numbers for total loops: >> >> lockref: w/o patch | w/ patch >> ====================== >> Run #1: 2.688.094 | 2.643.004 >> Run #2: 2.678.884 | 2.652.787 >> Run #3: 2.686.450 | 2.650.142 >> Run #4: 2.688.435 | 2.648.409 >> Run #5: 2.693.770 | 2.651.514 > > Yes, so this is pretty much expected. > > If you don't have a very high core count (you don't mention your > system, but that's pretty - I get ~65 million repetitions in 10 > seconds on my i5-670), the cmpxchg will not help - because you don't > actually see the bad "wait on spinlock" behavior in the first place. > > And a "cmpxchg" is slightly slower than the very optimized spinlocks, > and has that annoying "read original value" first issue too. So the > patch can make things a bit slower, although it will depends on the > microarchitecture (and as mentioned elsewhere, there are other things > that can make a bigger difference boot-to-boot - dentry allocation > details etc can have "sticky" performance impact). > > So we may take a small hit in order to then *not* have horrible > scalability at the high end. > A Samsung series-5 ultrabook. $ grep "model name" /proc/cpuinfo | uniq model name : Intel(R) Core(TM) i5-2467M CPU @ 1.60GHz - Sedat - -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
