Re: [PATCH 03/21] Remove use of signalfd in block-raw-posix.c

[Avi Kivity <avi@redhat.com>]

Anthony Liguori wrote:
> Avi Kivity wrote:
>> Anthony Liguori wrote:
>>> We don't use signalfd in upstream QEMU.  Instead, we always emulate it.
>>>   
>>
>> With an extra thread -> so an extra context switch.
>
> We don't use an extra thread.  We just install a signal handler that 
> writes to a pipe.  At best, the added overhead is that we get EINTRs 
> more often but this is something we already handle.

Oh okay.  But signal delivery is slow; for example the FPU needs to be 
reset.

> I'm not sure signalfd really buys us much.  To emulate it requires 
> writing a bunch more data to the pipe.  When writing more than 1 byte, 
> we have to worry about whether there's a partial write because the 
> pipe buffers full).  We also have to make sure to read from the fd in 
> properly sized chunks.

Then we can use one byte writes (and reads) when signalfd is not 
available.  128 byte pipe read/writes should always be atomic on Linux 
though, likely on other OSes too.

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