[dm-devel] [PATCH 1/5] blk-mq: introduce BLK_STS_DEV_RESOURCE
Bart Van Assche
Bart.VanAssche at wdc.com
Tue Jan 23 16:54:02 UTC 2018
On Wed, 2018-01-24 at 00:49 +0800, Ming Lei wrote:
> On Tue, Jan 23, 2018 at 04:47:11PM +0000, Bart Van Assche wrote:
> > On Wed, 2018-01-24 at 00:41 +0800, Ming Lei wrote:
> > > Could you explain where to call call_rcu()? call_rcu() can't be used in
> > > IO path at all.
> >
> > Can you explain what makes you think that call_rcu() can't be used in the
> > I/O path? As you know call_rcu() invokes a function asynchronously. From
> > Documentation/RCU/Design/Requirements/Requirements.html:
> >
> > The <tt>call_rcu()</tt> function may be used in a number of
> > situations where neither <tt>synchronize_rcu()</tt> nor
> > <tt>synchronize_rcu_expedited()</tt> would be legal,
> > including within preempt-disable code, <tt>local_bh_disable()</tt> code,
> > interrupt-disable code, and interrupt handlers.
>
> OK, suppose it is true, do you want to change most of STS_RESOURCE in
> all drivers to this way? Why can't we use the generic and simple approach
> in this patch?
Please reread my proposal. I did not propose to change any block drivers.
What I proposed is to change the blk_mq_delay_run_hw_queue() implementation
such that it uses call_rcu() instead of kblockd_mod_delayed_work_on().
That's a generic and simple approach.
Bart.
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