Re: [Qemu-devel] Linux SIGIO handling changes

[Avi Kivity <avi@qumranet.com>]

Anthony Liguori wrote:
> Anders Melchiorsen wrote:
>> I am resending this patch, split into two parts now.
>>
>> This cleans up SIGIO handling to improve latency:
>> - SIGALRM for alarm timers
>> - enable SIGIO on qemu_set_fd_handler2()
>>
>> The issue was found in KVM, where it is much more visible,
>> because there is no periodic timer. However, it has been
>> confirmed (by Aurelien Jarno) that even for qemu, this
>> approach "improves network transfers in a huge way".
>>
>> Please apply, or give a firm rejection so I can stop resending.
>>   
>
> Probably the right thing to do is the direction KVM is moving toward, 
> i.e. have a separate IO thread.
>
> Setting SIGIO on every file descriptor is really just a hack to break 
> out of the cpu exec loop.  It's unclear to me whether it's really 
> always the right thing to do for every file descriptor.
>

Even with a separate iothread one needs the signals, as there is no 
other race-free way to poll for both aio completions and fd readiness.

[well, pselect works, but I dislike it and it isn't present on all kernels]

-- 
error compiling committee.c: too many arguments to function