Date: Fri, 2 Mar 2018 16:43:15 -0800 From: bob prohaska <fbsd@www.zefox.net> To: Ian Lepore <ian@freebsd.org> Cc: Warner Losh <imp@bsdimp.com>, Mike <the.lists@mgm51.com>, "freebsd-arm@freebsd.org" <freebsd-arm@freebsd.org>, bob prohaska <fbsd@www.zefox.net> Subject: Re: Is maximum swap usage tunable? Message-ID: <20180303004315.GB37148@www.zefox.net> In-Reply-To: <1520010957.23690.10.camel@freebsd.org> References: <20180228170311.GA26187@www.zefox.net> <a759ecea-83f4-b0b2-7113-c39633f68637@mgm51.com> <20180228185517.GB26187@www.zefox.net> <8f422161-885e-aa91-eacd-018540222d65@mgm51.com> <20180228214301.GA29481@www.zefox.net> <b82801b8-bc29-414c-1170-621bb4a5d937@mgm51.com> <CANCZdfq_MpxjUyVd-=%2BMiAQAER4TeDh9irhx_evdXwa3yt3h0g@mail.gmail.com> <1520010957.23690.10.camel@freebsd.org>
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On Fri, Mar 02, 2018 at 10:15:57AM -0700, Ian Lepore wrote: > You forgot a cause: (5) swap is on an sdcard where taking 30-90 seconds > to complete an IO is "normal". > FWIW, the Sandisk Extreme USB flash drive is claimed to be considerably faster than that, ~2MB/sec random write, at least per http://usb.userbenchmark.com/SanDisk-Extreme-USB-30-16GB/Rating/1301 One hopes(!) that the microSD cards of the same name are simlar. > Making it even more fun, there's a sort of (5.5) bullet: an sdcard can > "lend" its horrible performance to every other storage device in the > system. ?If there is a ton of IO queued up to the sd device (such as > when .o files from a a make -j are ending up there) then all the > buffers in the system get stacked up in the sd device's bio queue and > IO to other devices suffers. > A j4 buildworld on an RPI2 running -current seems to work much better than j2 on an RPI3, both using the same Sandisk flash devices. The Pi2 has /usr, /var /tmp and swap on USB flash, the Pi3 has /tmp and half the swap on microSD, with /usr, /var and the other half of swap on USB flash. Thus, /tmp and all of swap are on the same device for the Pi2, while /tmp and only half the swap are on the same device on the Pi3. It was expected the Pi3 should work better than the Pi2, but the opposite seems to be observed. > I've always thought the new(ish) IO scheduler stuff should be able to > help with that in some way, but I never get around to looking at it. > > I'd be pleased to do any testing I can, if it helps. Thanks for reading, bob prohaska
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