Hi Michael, On Mon, Jun 08, 2020 at 08:52:51AM -0400, Michael S. Tsirkin wrote: > > > This adds infrastructure required for supporting > multiple ring formats. > > The idea is as follows: we convert descriptors to an > independent format first, and process that converting to > iov later. > > Used ring is similar: we fetch into an independent struct first, > convert that to IOV later. > > The point is that we have a tight loop that fetches > descriptors, which is good for cache utilization. > This will also allow all kind of batching tricks - > e.g. it seems possible to keep SMAP disabled while > we are fetching multiple descriptors. > > For used descriptors, this allows keeping track of the buffer length > without need to rescan IOV. > > This seems to perform exactly the same as the original > code based on a microbenchmark. > Lightly tested. > More testing would be very much appreciated. while testing the vhost-vsock I found some issues in vhost-net (the VM had also a virtio-net device). This is the dmesg of the host (it is a QEMU VM): [ 171.860074] CPU: 0 PID: 16613 Comm: vhost-16595 Not tainted 5.7.0-ste-12703-gaf7b4801030c-dirty #6 [ 171.862210] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014 [ 171.865998] Call Trace: [ 171.866440] <IRQ> [ 171.866817] dump_stack+0x57/0x7a [ 171.867440] nmi_cpu_backtrace.cold+0x14/0x54 [ 171.868233] ? lapic_can_unplug_cpu.cold+0x3b/0x3b [ 171.869153] nmi_trigger_cpumask_backtrace+0x85/0x92 [ 171.870143] arch_trigger_cpumask_backtrace+0x19/0x20 [ 171.871134] rcu_dump_cpu_stacks+0xa0/0xd2 [ 171.872203] rcu_sched_clock_irq.cold+0x23a/0x41c [ 171.873098] update_process_times+0x2c/0x60 [ 171.874119] tick_sched_timer+0x59/0x160 [ 171.874777] ? tick_switch_to_oneshot.cold+0x79/0x79 [ 171.875602] __hrtimer_run_queues+0x10d/0x290 [ 171.876317] hrtimer_interrupt+0x109/0x220 [ 171.877025] smp_apic_timer_interrupt+0x76/0x150 [ 171.877875] apic_timer_interrupt+0xf/0x20 [ 171.878563] </IRQ> [ 171.878897] RIP: 0010:vhost_get_avail_buf+0x5f8/0x860 [vhost] [ 171.879951] Code: 48 8b bb 88 00 00 00 48 85 ff 0f 84 ad 00 00 00 be 01 00 00 00 44 89 45 80 e8 24 52 08 c1 8b 43 68 44 8b 45 80 e9 e9 fb ff ff <45> 85 c0 0f 85 48 fd ff ff 48 8b 43 38 48 83 bb 38 45 00 00 00 48 [ 171.889938] RSP: 0018:ffffc90000397c40 EFLAGS: 00000246 ORIG_RAX: ffffffffffffff13 [ 171.896828] RAX: 0000000000000040 RBX: ffff88822c3f4688 RCX: ffff888231090000 [ 171.898903] RDX: 0000000000000440 RSI: ffff888231090000 RDI: ffffc90000397c80 [ 171.901025] RBP: ffffc90000397ce8 R08: 0000000000000001 R09: ffffc90000397dc4 [ 171.903136] R10: 000000231edc461f R11: 0000000000000003 R12: 0000000000000001 [ 171.905213] R13: 0000000000000001 R14: ffffc90000397dd4 R15: ffff88822c3f87a8 [ 171.907553] get_tx_bufs+0x49/0x180 [vhost_net] [ 171.909142] handle_tx_copy+0xb4/0x5c0 [vhost_net] [ 171.911495] ? update_curr+0x67/0x160 [ 171.913376] handle_tx+0xb0/0xe0 [vhost_net] [ 171.916451] handle_tx_kick+0x15/0x20 [vhost_net] [ 171.919912] vhost_worker+0xb3/0x110 [vhost] [ 171.923379] kthread+0x106/0x140 [ 171.925314] ? __vhost_add_used_n+0x1c0/0x1c0 [vhost] [ 171.933388] ? kthread_park+0x90/0x90 [ 171.936148] ret_from_fork+0x22/0x30 [ 234.859212] rcu: INFO: rcu_sched self-detected stall on CPU [ 234.860036] rcu: 0-....: (20981 ticks this GP) idle=962/1/0x4000000000000002 softirq=15513/15513 fqs=10340 [ 234.861547] (t=21003 jiffies g=24773 q=2390) [ 234.862158] NMI backtrace for cpu 0 [ 234.862638] CPU: 0 PID: 16613 Comm: vhost-16595 Not tainted 5.7.0-ste-12703-gaf7b4801030c-dirty #6 [ 234.864008] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014 [ 234.866084] Call Trace: [ 234.866395] <IRQ> [ 234.866648] dump_stack+0x57/0x7a [ 234.867079] nmi_cpu_backtrace.cold+0x14/0x54 [ 234.867679] ? lapic_can_unplug_cpu.cold+0x3b/0x3b [ 234.868322] nmi_trigger_cpumask_backtrace+0x85/0x92 [ 234.869013] arch_trigger_cpumask_backtrace+0x19/0x20 [ 234.869747] rcu_dump_cpu_stacks+0xa0/0xd2 [ 234.870267] rcu_sched_clock_irq.cold+0x23a/0x41c [ 234.870960] update_process_times+0x2c/0x60 [ 234.871578] tick_sched_timer+0x59/0x160 [ 234.872148] ? tick_switch_to_oneshot.cold+0x79/0x79 [ 234.872949] __hrtimer_run_queues+0x10d/0x290 [ 234.873711] hrtimer_interrupt+0x109/0x220 [ 234.874271] smp_apic_timer_interrupt+0x76/0x150 [ 234.874913] apic_timer_interrupt+0xf/0x20 [ 234.876507] </IRQ> [ 234.876799] RIP: 0010:vhost_get_avail_buf+0x8a/0x860 [vhost] [ 234.877828] Code: 8d 72 06 00 00 85 c0 0f 85 fb 02 00 00 8b 57 70 89 d0 2d 00 04 00 00 0f 88 72 06 00 00 45 31 c0 4c 8d bb 20 41 00 00 4d 89 ee <44> 0f b7 a3 08 01 00 00 66 44 3b a3 0a 01 00 00 0f 84 58 05 00 00 [ 234.882059] RSP: 0018:ffffc90000397c40 EFLAGS: 00000283 ORIG_RAX: ffffffffffffff13 [ 234.883227] RAX: 0000000000000040 RBX: ffff88822c3f4688 RCX: ffff888231090000 [ 234.884317] RDX: 0000000000000440 RSI: ffff888231090000 RDI: ffffc90000397c80 [ 234.886531] RBP: ffffc90000397ce8 R08: 0000000000000001 R09: ffffc90000397dc4 [ 234.891840] R10: 000000231edc461f R11: 0000000000000003 R12: 0000000000000001 [ 234.896670] R13: 0000000000000001 R14: ffffc90000397dd4 R15: ffff88822c3f87a8 [ 234.900918] get_tx_bufs+0x49/0x180 [vhost_net] [ 234.904280] handle_tx_copy+0xb4/0x5c0 [vhost_net] [ 234.916402] ? update_curr+0x67/0x160 [ 234.917688] handle_tx+0xb0/0xe0 [vhost_net] [ 234.918865] handle_tx_kick+0x15/0x20 [vhost_net] [ 234.920366] vhost_worker+0xb3/0x110 [vhost] [ 234.921500] kthread+0x106/0x140 [ 234.922219] ? __vhost_add_used_n+0x1c0/0x1c0 [vhost] [ 234.923595] ? kthread_park+0x90/0x90 [ 234.924442] ret_from_fork+0x22/0x30 [ 297.870095] rcu: INFO: rcu_sched self-detected stall on CPU [ 297.871352] rcu: 0-....: (36719 ticks this GP) idle=962/1/0x4000000000000002 softirq=15513/15513 fqs=18087 [ 297.873585] (t=36756 jiffies g=24773 q=2853) [ 297.874478] NMI backtrace for cpu 0 [ 297.875229] CPU: 0 PID: 16613 Comm: vhost-16595 Not tainted 5.7.0-ste-12703-gaf7b4801030c-dirty #6 [ 297.877204] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014 [ 297.881644] Call Trace: [ 297.882185] <IRQ> [ 297.882621] dump_stack+0x57/0x7a [ 297.883387] nmi_cpu_backtrace.cold+0x14/0x54 [ 297.884390] ? lapic_can_unplug_cpu.cold+0x3b/0x3b [ 297.885568] nmi_trigger_cpumask_backtrace+0x85/0x92 [ 297.886746] arch_trigger_cpumask_backtrace+0x19/0x20 [ 297.888260] rcu_dump_cpu_stacks+0xa0/0xd2 [ 297.889508] rcu_sched_clock_irq.cold+0x23a/0x41c [ 297.890803] update_process_times+0x2c/0x60 [ 297.893357] tick_sched_timer+0x59/0x160 [ 297.895143] ? tick_switch_to_oneshot.cold+0x79/0x79 [ 297.897832] __hrtimer_run_queues+0x10d/0x290 [ 297.899841] hrtimer_interrupt+0x109/0x220 [ 297.900909] smp_apic_timer_interrupt+0x76/0x150 [ 297.903543] apic_timer_interrupt+0xf/0x20 [ 297.906509] </IRQ> [ 297.908004] RIP: 0010:vhost_get_avail_buf+0x92/0x860 [vhost] [ 297.911536] Code: 85 fb 02 00 00 8b 57 70 89 d0 2d 00 04 00 00 0f 88 72 06 00 00 45 31 c0 4c 8d bb 20 41 00 00 4d 89 ee 44 0f b7 a3 08 01 00 00 <66> 44 3b a3 0a 01 00 00 0f 84 58 05 00 00 8b 43 28 83 e8 01 41 21 [ 297.930274] RSP: 0018:ffffc90000397c40 EFLAGS: 00000283 ORIG_RAX: ffffffffffffff13 [ 297.934056] RAX: 0000000000000040 RBX: ffff88822c3f4688 RCX: ffff888231090000 [ 297.938371] RDX: 0000000000000440 RSI: ffff888231090000 RDI: ffffc90000397c80 [ 297.944222] RBP: ffffc90000397ce8 R08: 0000000000000001 R09: ffffc90000397dc4 [ 297.953817] R10: 000000231edc461f R11: 0000000000000003 R12: 0000000000000001 [ 297.956453] R13: 0000000000000001 R14: ffffc90000397dd4 R15: ffff88822c3f87a8 [ 297.960873] get_tx_bufs+0x49/0x180 [vhost_net] [ 297.964163] handle_tx_copy+0xb4/0x5c0 [vhost_net] [ 297.965871] ? update_curr+0x67/0x160 [ 297.966893] handle_tx+0xb0/0xe0 [vhost_net] [ 297.968442] handle_tx_kick+0x15/0x20 [vhost_net] [ 297.971327] vhost_worker+0xb3/0x110 [vhost] [ 297.974275] kthread+0x106/0x140 [ 297.976141] ? __vhost_add_used_n+0x1c0/0x1c0 [vhost] [ 297.979518] ? kthread_park+0x90/0x90 [ 297.981665] ret_from_fork+0x22/0x30
