Date: Fri, 10 Jun 2016 08:38:36 -0700 From: Tim Kientzle <tim@kientzle.com> To: Gergely Imreh <imrehg@gmail.com> Cc: FreeBSD ARM <freebsd-arm@freebsd.org> Subject: Re: RPi2 i/o blocking and SD card performance Message-ID: <3AA7AD8C-E6E9-4E8E-96D2-5A712EBD8D52@kientzle.com> In-Reply-To: <CAJ3iQcoc5nVSFz3JKMG_Y9Q9k4PFizmp2rf3vfA7nv=u_12nBQ@mail.gmail.com> References: <CAJ3iQcoc5nVSFz3JKMG_Y9Q9k4PFizmp2rf3vfA7nv=u_12nBQ@mail.gmail.com>
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> On Jun 9, 2016, at 2:37 AM, Gergely Imreh <imrehg@gmail.com> wrote: >=20 > Hi, >=20 > I've been testing FreeBSD 11.0-CURRENT on a RaspberryPi2. I'm = relatively > new to FreeBSD, and wondering if there's any advice for improving the > performance a bit. >=20 > First, it looks like there's a lot of i/o blocking behaviour going on. = For > example running MediaWiki on the board, if I compile any ports, the = site > itself is pretty much unusable (the PHP scripts time out even with = 180s > timeouts). The strangest thing is that the CPU usage is not at 100% = all the > way, can be that all 4 cores are ~99% idle, and still everything goes = very > slow. Once the ports compilation or any other i/o-related task is = finished, > it's snappy again. >=20 > Any idea why it could be to have such big latency/lag even though the = CPU > is idle? Is there anything I could test? Watch vmstat output for a while during these periods. In the past, = I=E2=80=99ve noticed the CPU alternating between being completely busy and completely idle. When I last asked about this, I recall someone pointing to the = disk buffer management as the culprit =E2=80=94 apparently, with slow devices such = as SD cards it tends to accumulate pending writes, then everything blocks while the = disk cache drains. But I may have misunderstood... Tim
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