Re: [PATCH 02/12] pci-p2p: Add sysfs group to display p2pmem stats

[Logan Gunthorpe]

On 04/01/18 02:50 PM, Bjorn Helgaas wrote:

On Thu, Jan 04, 2018 at 12:01:27PM -0700, Logan Gunthorpe wrote:

Attributes display the total amount of P2P memory, the ammount available
and whether it is published or not.


s/ammount/amount/ (also below)


Will fix.


I wonder if "p2pdma" would be a more suggestive term?  It's not really
the *memory* that is peer-to-peer; the peer-to-peer part is referring
to *access* to the memory.


I agree with Jason on this point. For now, it only describes the 
peer-to-peer memory attributes. If we change the directory to p2pdma 
then we'd have to add a mem prefix or something to each attribute.



@@ -82,6 +130,9 @@ static int pci_p2pmem_setup(struct pci_dev *pdev)
if (error)
goto out_pool_destroy;
  
+	if (sysfs_create_group(>dev.kobj, _group))

+   dev_warn(>dev, "failed to create p2p sysfs group\n");


Not sure the warning (by itself) is worthwhile.  If we were going to
disable the feature if sysfs_create_group() failed, that's one thing,
but we aren't doing anything except generating a warning, which the
user can't really do anything with.  If the user is looking for the
sysfs file, its absence will be obvious even without the message.


Unfortunately, sysfs_create_group() has the warn_unused_result flag set. 
So I need to do something with the result to squash the warning. I could 
just assign it to an unused variable but something seemed like it needed 
to be done and printing a warning was the easiest thing...


Logan

___
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm

Re: [PATCH 02/12] pci-p2p: Add sysfs group to display p2pmem stats

[Jason Gunthorpe]

On Thu, Jan 04, 2018 at 03:50:40PM -0600, Bjorn Helgaas wrote:
> > This is similar to /sys/bus/pci/drivers_autoprobe, but
> > affects only the VFs associated with a specific PF.
> > +
> > +What:  /sys/bus/pci/devices/.../p2pmem/available
> 
> I wonder if "p2pdma" would be a more suggestive term?  It's not really
> the *memory* that is peer-to-peer; the peer-to-peer part is referring
> to *access* to the memory.

There have been out of tree patches using P2P DMA for a long time, and
some of the use cases have nothing to do with 'memory' - eg DMA to
'registers'

I notice that this series particularly focus on treating the target
BAR as 'memory' - ie it puts genalloc on top of the BAR, and I guess
treat all addresses as equal and interchangable.

If this series gets accepted I would expect proposals to extend this
infrastructure to allow for P2P for registers in some way as well.

So I think the 'p2pmem' name is a good choice only when it is in
places that talk about the genalloc part of this design.

We should reserve p2pdma to talk about the generic infrastructure
unrelated to the genalloc pool.

Since these sysfs's seem to report the genalloc pool status, p2pmem
seems like a good choice to me.

> > @@ -82,6 +130,9 @@ static int pci_p2pmem_setup(struct pci_dev *pdev)
> > if (error)
> > goto out_pool_destroy;
> >  
> > +   if (sysfs_create_group(>dev.kobj, _group))
> > +   dev_warn(>dev, "failed to create p2p sysfs group\n");
> 
> Not sure the warning (by itself) is worthwhile.  If we were going to
> disable the feature if sysfs_create_group() failed, that's one thing,
> but we aren't doing anything except generating a warning, which the
> user can't really do anything with.  If the user is looking for the
> sysfs file, its absence will be obvious even without the message.

Don't most of the failure paths inside sysfs_create_group cause prints
anyhow?

Jason
___
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm

Re: [PATCH 02/12] pci-p2p: Add sysfs group to display p2pmem stats

[Bjorn Helgaas]

On Thu, Jan 04, 2018 at 12:01:27PM -0700, Logan Gunthorpe wrote:
> Attributes display the total amount of P2P memory, the ammount available
> and whether it is published or not.

s/ammount/amount/ (also below)

> Signed-off-by: Logan Gunthorpe 
> ---
>  Documentation/ABI/testing/sysfs-bus-pci | 25 
>  drivers/pci/p2p.c   | 51 
> +
>  2 files changed, 76 insertions(+)
> 
> diff --git a/Documentation/ABI/testing/sysfs-bus-pci 
> b/Documentation/ABI/testing/sysfs-bus-pci
> index 44d4b2be92fd..7b80ea77faca 100644
> --- a/Documentation/ABI/testing/sysfs-bus-pci
> +++ b/Documentation/ABI/testing/sysfs-bus-pci
> @@ -323,3 +323,28 @@ Description:
>  
>   This is similar to /sys/bus/pci/drivers_autoprobe, but
>   affects only the VFs associated with a specific PF.
> +
> +What:/sys/bus/pci/devices/.../p2pmem/available

I wonder if "p2pdma" would be a more suggestive term?  It's not really
the *memory* that is peer-to-peer; the peer-to-peer part is referring
to *access* to the memory.

> @@ -82,6 +130,9 @@ static int pci_p2pmem_setup(struct pci_dev *pdev)
>   if (error)
>   goto out_pool_destroy;
>  
> + if (sysfs_create_group(>dev.kobj, _group))
> + dev_warn(>dev, "failed to create p2p sysfs group\n");

Not sure the warning (by itself) is worthwhile.  If we were going to
disable the feature if sysfs_create_group() failed, that's one thing,
but we aren't doing anything except generating a warning, which the
user can't really do anything with.  If the user is looking for the
sysfs file, its absence will be obvious even without the message.

>   pdev->p2p = p2p;
>  
>   return 0;
> -- 
> 2.11.0
> 
___
Linux-nvdimm mailing list
Linux-nvdimm@lists.01.org
https://lists.01.org/mailman/listinfo/linux-nvdimm