Re: barriers vs. reads

[Werner Almesberger <wa@almesberger.net>]

Jens Axboe wrote:
> I don't think a read-barrier currently has a meaning. A write barrier
> will force ordering for later reads too, of course.

That's one of the problem spots with priorities: if there are a
lot of writes in the queue, high-priority reads will be delayed
for a long time.

But do we have cases where reads must not cross write barriers ?

> It can't, the insert position doesn't tell you whether it's a barrier or
> not. You have to check ->flags for that.

Yet deadline, AS, and CFQ don't do any such check :-)

- Werner

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 / Werner Almesberger, Buenos Aires, Argentina         wa@almesberger.net /
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