Date: Mon, 13 Oct 2003 22:55:19 -0600 (MDT) From: "M. Warner Losh" <imp@bsdimp.com> To: nate@root.org Cc: current@freebsd.org Subject: Re: Interrupt statistics? Message-ID: <20031013.225519.19308181.imp@bsdimp.com> In-Reply-To: <20031013105145.J28323@root.org> References: <20031011234314.P23991@root.org> <20031012.095503.129593225.imp@bsdimp.com> <20031013105145.J28323@root.org>
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In message: <20031013105145.J28323@root.org>
Nate Lawson <nate@root.org> writes:
: Given that, my biggest concern now is IO corruption. Are there any
: devices that have a low interrupt rate (or bus mastering rate) that cannot
: handle a few hundred us latency added to their handler startup? I'm
: thinking something like a floppy drive where the time between interrupts
: is great enough that cpu_idle() is called but that need to be serviced
: quickly or data is over/underrun.
sio/uart
At 115200 baud, you have 173us to service the interrupt when the FIFO
interrupt level is set to HI. At 460800 at HI you have 43us. With
the more conservative MED settings, these numbers are 4 times better
(670us and 173us). 200us is smack dab in the middle of these times.
This is inbound data, so things could be idle and there be issues.
Not sure about other devices.
Warner
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