Date: Thu, 19 Jul 2018 10:45:04 +0100 From: Pete French <petefrench@ingresso.co.uk> To: freebsd-stable@freebsd.org Subject: An oddity of memory speeds and timings Message-ID: <E1fg5Ue-0009ot-42@dilbert.ingresso.co.uk>
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Yesterday I inreased my memory speed on my Ryzen box from 2133 to 2400 as I had previously been underclocking it. Ryzens are sensetive to memory clock speed as it affects the speed of the underlying fabric between the cores as well as I understand it, so worth running it at its rated speed. I meausred the improvement by using 'time' on a CPU bound compile. It speeded wall clock time up by abotu the expected amount, but what I found curious looking at the breakdown of the timings reported by time was that. there was no reduction in user time, but a drastic reduction (25%!) in system time. Can anyone explain that ? My only wild theory at the moment is that for a single process the user space component is single threaded and shows no real improvement, but the kerenl, being multi-threaded, will benifit from the speedup of the interconnect between the cores. But I dont know if the timings measures by time wuld actually show that. Interesting though. -pete.
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