lkml.org 
[lkml]   [2009]   [Aug]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH 0/2] eventfd: new EFD_STATE flag
On 08/20/2009 07:44 PM, Davide Libenzi wrote:
> On Thu, 20 Aug 2009, Avi Kivity wrote:
>
>> On 08/20/2009 07:20 PM, Davide Libenzi wrote:
>>>
>>> I briefly looked at this while in vacation, although I did not reply
>>> hoping the horrible feeling about this code would go away.
>>> It didn't.
>>> I find this to be an ugly and ad-hoc multiplexing of eventfd with added
>>> functionalities of questionable general use.
>>> I'm pretty sure you can do better on KVM side, to solve the problem w/out
>>> littering eventfd.
>>
>> While we could argue about this my feeling is that we should drop this, at
>> least until we can quantify what benefit it has and whether there are any
>> Davide-acceptable alternatives.
>
> I really didn't mean to be harsh, but seriously, we cannot just have a
> Multiplexing Feast over eventfd, with one-time users.

EFD_STATE actually does two changes: a) makes read block until the value
changes; b) makes each write override the previous one. How would you
feel if the two changes were separated? I can see each of them has use
cases

For example, (a) could be implemented by using select's xfds (POLLPRI)
to poll for value changes (rfds would still poll for non-zeroness).
Then Michael does not need even to read the eventfd; instead he'd check
POLLIN with a zero timeout.

(b) could be implemented with a flag like Michael did.

Paolo


\
 
 \ /
  Last update: 2009-08-20 19:59    [W:0.053 / U:0.420 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site