Re: [Qemu-devel] [PATCH] 8250: more realistic TX-done IRQ rate

[Jan Kiszka <jan.kiszka@web.de>]

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Jan Kiszka wrote:
> Paul Brook wrote:
>> On Saturday 12 April 2008, Jan Kiszka wrote:
>> I'd also expect you to have the same problem with the RX queue. If you
>> don't it's a bug elsewhere in qemu.
>>
>>> +            qemu_mod_timer(s->tx_timer, 1000 / (11520 / s->divider));
>>
>> This looks bogus. I think you're a few orders of magnitude out in your
>> timing calculations.  As mentioned above, in practice you unlikely to
>> get anywhere
>> near the necessary realtime performance out of qemu.
> 
> That depends. Current Linux distros typically have
> CONFIG_HIGH_RES_TIMERS enabled. But, of course, not many OSes QEMU works
> on have such support at all, and even Linux may decided to work without
> it for various reasons.

OK, that line was totally bogus. Somehow I once assumed that
qemu_mod_timer takes relative timeout (though I've used it with absolute
dates before). A new version will follow soon, which in fact triggered a
second patch for another issue of the current emulation - the hard-coded
baudbase.

Jan


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