Date: Sun, 1 Apr 2018 10:33:54 -0600 From: Warner Losh <imp@bsdimp.com> To: Stefan Esser <se@freebsd.org> Cc: FreeBSD Current <freebsd-current@freebsd.org> Subject: Re: Extremely low disk throughput under high compute load Message-ID: <CANCZdfoieekesqKa5RmOp=z2vycsVqnVss7ROnO87YTV-qBUzA@mail.gmail.com> In-Reply-To: <dc8d0285-1916-6581-2b2d-e8320ec3d894@freebsd.org> References: <dc8d0285-1916-6581-2b2d-e8320ec3d894@freebsd.org>
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On Sun, Apr 1, 2018 at 9:18 AM, Stefan Esser <se@freebsd.org> wrote: > My i7-2600K based system with 24 GB RAM was in the midst of a buildworld > -j8 > (starting from a clean state) which caused a load average of 12 for more > than > 1 hour, when I decided to move a directory structure holding some 10 GB to > its > own ZFS file system. File sizes varied, but were mostly in the range 0f > 500KB. > > I had just thrown away /usr/obj, but /usr/src was cached in ARC and thus > there > was nearly no disk activity caused by the buildworld. > > The copying proceeded at a rate of at most 10 MB/s, but most of the time > less > than 100 KB/s were transferred. The "cp" process had a PRIO of 20 and thus > a > much better priority than the compute bound compiler processes, but it got > just 0.2% to 0.5% of 1 CPU core. Apparently, the copy process was scheduled > at such a low rate, that it only managed to issue a few controller writes > per > second. > > The system is healthy and does not show any problems or anomalies under > normal use (e.g., file copies are fast, without the high compute load). > > This was with SCHED_ULE on a -CURRENT without WITNESS or malloc debugging. > > Is this a regression in -CURRENT? > Does 'sync' push a lot of I/O to the disk? Is the effective throughput of CP tiny or large? It's tiny, if I read right, and the I/O is slow (as opposed to it all buffering in memory and being slow to drain own), right? Warner
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