On 2011-04-27 14:12, Avi Kivity wrote: > On 04/27/2011 02:21 PM, Jan Kiszka wrote: >> On 2011-04-27 11:14, Avi Kivity wrote: >>> On 04/27/2011 12:06 PM, Jan Kiszka wrote: >>>>> >>>>> We can simply drop all route entries that are used exclusively in qemu >>>>> (i.e. not bound to an irqfd) and let the cache rebuild itself. >>>> >>>> When should they be dropped? >>> >>> Whenever we need to allocate a new routing entry, but cannot because it >>> is full. >>> >>> def kvm_send_msi_message(addr, val): >>> gsi = route_cache.get((addr, val), None) >>> if gsi is None: >>> expire_volatile_route_cache_entries_if_full() >>> gsi = alloc_gsi_cache_entry() >>> route_cache[(addr, val)] = gsi >>> update_route_cache() >>> kvm_irq_line(gsi, 1) >>> kvm_irq_line(gsi, 0) >>> >>> The code would have to be in kvm.c, where it can track whether an entry >>> is volatile or persistent. >> >> Yeah, what I forgot is the other side of this caching: Looking up the >> GSI from the MSI addr/data tuple. That's more complex than the current >> O(1) way via device.msitable[vector]. Well, we could use some hash >> table. But is it worth it? IMHO only if we could radically simplify the >> PCI device hooking as well (HPET is negligible compared to that). But >> I'm not yet sure if we can given what vhost needs. > > A hash table is indeed overcomplicated for this. > > How about a replacement for stl_phys() for the MSI case: > > - stl_phys(timer->fsb >> 32, timer->fsb & 0xffffffff); > + msi_stl_phys(timer->fsb >> 32, timer->fsb & 0xffffffff, > &timer->msi_cache); > > msi_stl_phys(target_phys_addr_t addr, uint32_t data, MSICache *cache) > { > if (kvm_msi_enabled() && addr & MSI_ADDR_MASK == msi_base_addr) { > if (cache->addr != addr || cache->data != data) { > kvm_update_msi_cache(cache, addr, data); > } > kvm_irq_line(cache->gsi, 1); > kvm_irq_line(cache->gsi, 0); > return; > } > stl_phys(addr, data); > } I was planning for a MSI short-path anyway. Also for TCG, it's pointless to go through lengthy stl_phys if we know it's supposed to be an MSI message. > > This bit of code would need to be updated for IOMMU and interrupt > remapping, Quite a bit updates required for that anyway. > but at least it means that devices don't need significant > change for kvm support. We could also allocate a single gsi for use in > hw/apic.c so hacks like using DMA to generate an MSI will work (will be > slow, though). Needs some thoughts, maybe it will work. Though, it's not yet clear to me if we can drop the kvm hooks from msi/msix.c and still support vhost/dev-assignment this way. Just to keep hpet.c cleaner, I don't think it's worth the effort. Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html