[ovs-dev] [PATCH 2/2] netdev-dpdk: Allocate vhost_id dynamically.

[Ben Pfaff]

On Wed, Apr 10, 2019 at 05:35:34PM +0100, Ian Stokes wrote:
> On 4/10/2019 5:21 PM, Ian Stokes wrote:
> > On 3/5/2019 4:28 PM, Ilya Maximets wrote:
> > > 'vhost_id' is an array of 'PATH_MAX' bytes in the middle of
> > > 'netdev_dpdk' structure. That is 4K bytes.
> > > 
> > > 'vhost_id' never used on a hot path and there is no need to keep
> > > it inside the structure memory. Dynamic allocation will allow to
> > > decrease 'struct netdev_dpdk' signigficantly, saving 4KB per ETH
> > signigficantly -> significantly
> > > port (ETH ports doesn't use 'vhost_id') and almost same value per
> > > vhost ports (real 'vhost_id's, in common case, are much shorter).
> > > We could save the pointer space by making the union with 'devargs'
> > > which is mutually exclusive with 'vhost_id'.
> > > As we're just removing the single 'PADDED_MEMBER', the total
> > > cacheline layout is not affected.
> > > 
> > > Stats for 'struct netdev_dpdk':
> > > 
> > >      Before: /* size: 4992, cachelines: 78 */
> > >      After : /* size:  896, cachelines: 14 */
> > > 
> > 
> > Thanks Ilya, this looks like a good change, validated without issue.
> > 
> > I've addressed a minor typo in the commit message and comment style
> > issue below. Other than that it looks good so applied to master.
> > 
> > On a broader note, do you think it's worth capturing changes such as
> > this for users in documentation? i.e. previously the vhost-id path was
> > limited to 4096 (however unlikely it was that someone would exceed
> > this), but it wasn't captured in the OVS documentation from what I can
> > see. From a usability point is it something to document between the 2.10
> > and 2.11 release?
> > 
> 
> Sorry, meant OVS 2.11 to 2.12 above.

I like to document user-visible changes, but I think in this case it is
unlikely to fix any real user problems.  (It would be different if we
made this change in response to a user having a problem with a very long
vhost-id path.)