On Tue, Feb 22, 2022 at 04:55:41PM -0800, Luis Chamberlain wrote:
> On Thu, Feb 17, 2022 at 06:29:01PM +0530, Nitesh Shetty wrote:
> > Thu, Feb 17, 2022 at 01:07:00AM -0800, Luis Chamberlain wrote:
> > > The subject says limits for copy-offload...
> > >
> > > On Mon, Feb 14, 2022 at 01:29:52PM +0530, Nitesh Shetty wrote:
> > > > Add device limits as sysfs entries,
> > > > - copy_offload (RW)
> > > > - copy_max_bytes (RW)
> > > > - copy_max_hw_bytes (RO)
> > > > - copy_max_range_bytes (RW)
> > > > - copy_max_range_hw_bytes (RO)
> > > > - copy_max_nr_ranges (RW)
> > > > - copy_max_nr_ranges_hw (RO)
> > >
> > > Some of these seem like generic... and also I see a few more max_hw ones
> > > not listed above...
> > >
> > queue_limits and sysfs entries are differently named.
> > All sysfs entries start with copy_* prefix. Also it makes easy to lookup
> > all copy sysfs.
> > For queue limits naming, I tried to following existing queue limit
> > convention (like discard).
>
> My point was that your subject seems to indicate the changes are just
> for copy-offload, but you seem to be adding generic queue limits as
> well. Is that correct? If so then perhaps the subject should be changed
> or the patch split up.
>
Yeah, queue limits indicates copy offload. I think will make more
readable by adding copy_offload_* prefix.
> > > > +static ssize_t queue_copy_offload_store(struct request_queue *q,
> > > > + const char *page, size_t count)
> > > > +{
> > > > + unsigned long copy_offload;
> > > > + ssize_t ret = queue_var_store(©_offload, page, count);
> > > > +
> > > > + if (ret < 0)
> > > > + return ret;
> > > > +
> > > > + if (copy_offload && !q->limits.max_hw_copy_sectors)
> > > > + return -EINVAL;
> > >
> > >
> > > If the kernel schedules, copy_offload may still be true and
> > > max_hw_copy_sectors may be set to 0. Is that an issue?
> > >
> >
> > This check ensures that, we dont enable offload if device doesnt support
> > offload. I feel it shouldn't be an issue.
>
> My point was this:
>
> CPU1 CPU2
> Time
> 1) if (copy_offload
> 2) ---> preemption so it schedules
> 3) ---> some other high priority task Sets q->limits.max_hw_copy_sectors to 0
> 4) && !q->limits.max_hw_copy_sectors)
>
> Can something bad happen if we allow for this?
>
>
max_hw_copy_sectors is read only for user. And inside kernel, this is set
only by driver at initialization.
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