Re: [RFC net-next 1/2] ethtool: add support for controling the type of adaptive coalescing

[tanhuazhong]

On 2020/11/19 12:15, Andrew Lunn wrote:
> > diff --git a/include/uapi/linux/ethtool.h b/include/uapi/linux/ethtool.h
> > index 9ca87bc..afd8de2 100644
> > --- a/include/uapi/linux/ethtool.h
> > +++ b/include/uapi/linux/ethtool.h
> > @@ -433,6 +433,7 @@ struct ethtool_modinfo {
> >    *	a TX interrupt, when the packet rate is above @pkt_rate_high.
> >    * @rate_sample_interval: How often to do adaptive coalescing packet rate
> >    *	sampling, measured in seconds.  Must not be zero.
> > + * @use_dim: Use DIM for IRQ coalescing, if adaptive coalescing is enabled.
> >    *
> >    * Each pair of (usecs, max_frames) fields specifies that interrupts
> >    * should be coalesced until
> > @@ -483,6 +484,7 @@ struct ethtool_coalesce {
> >   	__u32	tx_coalesce_usecs_high;
> >   	__u32	tx_max_coalesced_frames_high;
> >   	__u32	rate_sample_interval;
> > +	__u32	use_dim;
> >   };
>
> You cannot do this.
>
> static noinline_for_stack int ethtool_set_coalesce(struct net_device *dev,
>                                                     void __user *useraddr)
> {
>          struct ethtool_coalesce coalesce;
>          int ret;
>
>          if (!dev->ethtool_ops->set_coalesce)
>                  return -EOPNOTSUPP;
>
>          if (copy_from_user(&coalesce, useraddr, sizeof(coalesce)))
>                  return -EFAULT;
>
> An old ethtool binary is not going to set this extra last byte to
> anything meaningful. You cannot tell if you have an old or new user
> space, so you have no idea if it put anything into use_dim, or if it
> is random junk.
>
> You have to leave the IOCTL interface unchanged, and limit this new
> feature to the netlink API.

Hi, Andrew.
thanks for pointing out this problem, i will fix it.
without callling set_coalesce/set_coalesce of ethtool_ops, do you have 
any suggestion for writing/reading this new attribute to/from the 
driver? add a new field in net_device or a new callback function in 
ethtool_ops seems not good.

> > diff --git a/include/uapi/linux/ethtool_netlink.h b/include/uapi/linux/ethtool_netlink.h
> > index e2bf36e..e3458d9 100644
> > --- a/include/uapi/linux/ethtool_netlink.h
> > +++ b/include/uapi/linux/ethtool_netlink.h
> > @@ -366,6 +366,7 @@ enum {
> >   	ETHTOOL_A_COALESCE_TX_USECS_HIGH,		/* u32 */
> >   	ETHTOOL_A_COALESCE_TX_MAX_FRAMES_HIGH,		/* u32 */
> >   	ETHTOOL_A_COALESCE_RATE_SAMPLE_INTERVAL,	/* u32 */
> > +	ETHTOOL_A_COALESCE_USE_DIM,			/* u8 */
>
> This appears to be a boolean? So /* flag */ would be better. Or do you
> think there is scope for a few different algorithms, and an enum would
> be better. If so, you should add the enum with the two current
> options.
>
> 	Andrew

ok, boolean seems enough.

Thanks.
Huazhong.
> .