.snip.. > > > > Lets break this down: > > > > > > > > How does the performance improve for one single device if you increase > > > > the SWIOTLB? > > > > Is there a specific device/driver that you can talk about that improve > > > > with this patch? > > > > > > > > > > > > > > Yes, these are mainly for multi-queue devices such as NICs or even > > > multi-queue virtio. > > > > > > This basically improves performance with concurrent DMA, hence, > > > basically multi-queue devices. > > > > OK, and for _1GB_ guest - what are the "internal teams/external customers" > > amount > > of CPUs they use? Please lets use real use-cases. > > >> I am sure you will understand we cannot share any external customer > >> data as all that customer information is proprietary. > >> > >> In similar situation if you have to share Oracle data, you will > >> surely have the same concerns and i don't think you will be able > >> to share any such information externally, i.e., outside Oracle. > >> > >I am asking for a simple query - what amount of CPUs does a 1GB > >guest have? The reason for this should be fairly obvious - if > >it is a 1vCPU, then there is no multi-queue and the existing > >SWIOTLB pool size as it is OK. > > > >If however there are say 2 and multiqueue is enabled, that > >gives me an idea of how many you use and I can find out what > >the maximum pool size usage of virtio there is with that configuration. > > Again we cannot share any customer data. > > Also i don't think there can be a definitive answer to how many vCPUs a > 1GB guest will have, it will depend on what kind of configuration we are > testing. > > For example, i usually setup 4-16 vCPUs for as low as 512M configured > gueest memory.
Sure, but you are not the normal user. That is I don't like that for 1GB guests your patch ends up doubling the SWIOTLB memory pool. That seems to me we are trying to solve a problem that normal users will not hit. That is why I want 'here is the customer bug'. Here is what I am going to do - I will take out the 1GB and 4GB case out of your patch and call it a day. If there are customers who start reporting issues we can revist that. Nothing wrong with 'Reported-by' XZY (we often ask the customer if he or she would like to be recognized on upstream bugs). And in the meantime I am going to look about adding .. > > I have been also testing with 16 vCPUs configuration for 512M-1G guest > memory with Mellanox SRIOV NICs, and this will be a multi-queue NIC > device environment. .. late SWIOTLB expansion to stich the DMA pools together as both Mellanox and VirtIO are not 32-bit DMA bound. > > So we might be having less configured guest memory, but we still might > be using that configuration with I/O intensive workloads. > > Thanks, > Ashish