On Wed, 14 Feb 2007, Ingo Molnar wrote:
>
> * Evgeniy Polyakov <[email protected]> wrote:
>
> > Let me clarify what I meant. There is only limited number of threads,
> > which are supposed to execute blocking context, so when all they are
> > used, main one will block too - I asked about possibility to reuse the
> > same thread to execute queue of requests attached to it, each request
> > can block, but if blocking issue is removed, it would be possible to
> > return.
>
> ah, ok, i understand your point. This is not quite possible: the
> cachemisses are driven from schedule(), which can be arbitraily deep
> inside arbitrary system calls. It can be in a mutex_lock() deep inside a
> driver. It can be due to a alloc_pages() call done by a kmalloc() call
> done from within ext3, which was called from the loopback block driver,
> which was called from XFS, which was called from a VFS syscall.
>
> Even if it were possible to backtrack i'm quite sure we dont want to do
> this, for three main reasons:
IMO it'd be quite simple. We detect the service-thread full condition,
*before* entering exec_atom and we queue the atom in an async_head request
list. Yes, there is the chance that from the test time in sys_async_exec,
to the time we'll end up entering exec_atom and down to schedule, one
of the threads would become free, but IMO better that blocking
sys_async_exec.
- Davide
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