Re: [PATCH 15/19] workqueue: reimplement workqueue flushing using color coded works

Tejun Heo
2009-10-01T17:17:33Z

Tejun Heo wrote:
> Hello, Linus.
>
> Linus Torvalds wrote:
>> On Thu, 1 Oct 2009, Tejun Heo wrote:
>>> Reimplement workqueue flushing using color coded works. There are two
>>> colors and each cwq has the current color which is painted on the
>>> works being issued via the cwq. Flushing a workqueue is achieved by
>>> flipping the current colors of each cwq and wait for the works which
>>> have the old color to drain.
>> Is there any reason for the "two colors" choice? I could imagine that it
>> could end up being a limitation (and possible deadlock?) to allow just a
>> single flush pending at any time.
>>
>> Could the color be an 8-bit counter or something like that instead?
>
> It's related to how many bits can be used from work_struct->data which
> in turn is determined by the alignment of cwq. Currently, the
> alignment is 8 bytes so 3 bits are available. One is used for
> PENDING, the other for LINKED and one last bit is used for COLOR.
> Aligning cwq to, say, 64bytes wouldn't be bad at all and then we can
> have 6-bits of coloring. Hmmm... yeap, I'll work on that.

Oops, 4 not 6.

--
tejun