On Fri, Mar 18, 2016 at 08:56:56AM +0100, Thomas Huth wrote: > On 17.03.2016 23:33, David Gibson wrote: > > On Thu, Mar 17, 2016 at 04:15:38PM +0100, Thomas Huth wrote: > >> On 17.03.2016 08:30, Thomas Huth wrote: > >>> On 17.03.2016 07:23, David Gibson wrote: > >>>> On Wed, Mar 16, 2016 at 01:16:50PM +0100, Thomas Huth wrote: > >>>>> > >>>>> This patch introduces an alternate way of handling the receive > >>>>> buffers of the spapr-vlan device, resulting in much better > >>>>> receive performance for the guest. > >> [...] > >>>>> +/** > >>>>> + * Enqueuing receive buffer by adding it to one of our receive buffer > >>>>> pools > >>>>> + */ > >>>>> +static target_long spapr_vlan_add_rxbuf_to_pool(VIOsPAPRVLANDevice > >>>>> *dev, > >>>>> + target_ulong buf) > >>>>> +{ > >>>>> + int size = VLAN_BD_LEN(buf); > >>>>> + int pool; > >>>>> + > >>>>> + pool = spapr_vlan_get_rx_pool_id(dev, size); > >>>>> + > >>>>> + /* No matching pool found? Try to create a new one */ > >>>>> + if (pool < 0) { > >>>>> + for (pool = RX_MAX_POOLS - 1; pool >= 0 ; pool--) { > >>>> > >>>> I don't think this loop actually accomplishes anything. Either the > >>>> last slot is free, in which case you use it, then sort into place, or > >>>> it's not, in which case you've hit the maximum number of buffer pools. > >>> > >>> Oh, you're right. Well spotted! I'll rework my patch to do it without > >>> that loop. > >> > >> Wait, no, there was a case where this loop is actually really required: > >> > >> 1) All pools are in use and filled with at least one BD > >> 2) User in the guest suddenly decides to change the buffer size of > >> one of the pools in the /sys fs of the guest. > >> 3) Guest driver tries to add buffers with a new size that do not > >> match any size of one of the pools in the host > >> 4) After the pool on the host runs empty which contained the BDs with > >> the size that is not in use anymore, we should recycle that pool > >> for the buffers with the new size instead. Since that buffer pool > >> might not be at the end of the list, we've got to scan all buffers > >> here to make sure we find it. > >> > >> So I think the for-loop should stay as it is. > > > > Ah, good point. I think I was assuming that the pools got sorted when > > one was emptied as well, but they're not and I suspect it's not a good > > idea to do so. > > > > Hmm.. I wonder if there's a brief way of explaining the above to put > > in the comment. > > Something like: > > /* > * If the guest used all pools, but changed the size of one pool > * inbetween, we might need to recycle that pool here (if it has > * already been emptied). Thus we need to scan all buffer pools > * here, not only the last one (which has the highest probability > * of being empty) > */ > > ? > > Or is that too verbose already?
Eh, it's written might as well throw it in. -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson
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