5.10-stable review patch. If anyone has any objections, please let me know.
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From: Haiyang Zhang haiyangz@microsoft.com
[ Upstream commit 7c9ff3deeee61b253715dcf968a6307af148c9b2 ]
The vmbus module uses a rotational algorithm to assign target CPUs to a device's channels. Depending on the timing of different device's channel offers, different channels of a device may be assigned to the same CPU.
For example on a VM with 2 CPUs, if NIC A and B's channels are offered in the following order, NIC A will have both channels on CPU0, and NIC B will have both channels on CPU1 -- see below. This kind of assignment causes RSS load that is spreading across different channels to end up on the same CPU.
Timing of channel offers: NIC A channel 0 NIC B channel 0 NIC A channel 1 NIC B channel 1
VMBUS ID 14: Class_ID = {f8615163-df3e-46c5-913f-f2d2f965ed0e} - Synthetic network adapter Device_ID = {cab064cd-1f31-47d5-a8b4-9d57e320cccd} Sysfs path: /sys/bus/vmbus/devices/cab064cd-1f31-47d5-a8b4-9d57e320cccd Rel_ID=14, target_cpu=0 Rel_ID=17, target_cpu=0
VMBUS ID 16: Class_ID = {f8615163-df3e-46c5-913f-f2d2f965ed0e} - Synthetic network adapter Device_ID = {244225ca-743e-4020-a17d-d7baa13d6cea} Sysfs path: /sys/bus/vmbus/devices/244225ca-743e-4020-a17d-d7baa13d6cea Rel_ID=16, target_cpu=1 Rel_ID=18, target_cpu=1
Update the vmbus CPU assignment algorithm to avoid duplicate CPU assignments within a device.
The new algorithm iterates num_online_cpus + 1 times. The existing rotational algorithm to find "next NUMA & CPU" is still here. But if the resulting CPU is already used by the same device, it will try the next CPU. In the last iteration, it assigns the channel to the next available CPU like the existing algorithm. This is not normally expected, because during device probe, we limit the number of channels of a device to be <= number of online CPUs.
Signed-off-by: Haiyang Zhang haiyangz@microsoft.com Reviewed-by: Michael Kelley mikelley@microsoft.com Tested-by: Michael Kelley mikelley@microsoft.com Link: https://lore.kernel.org/r/1626459673-17420-1-git-send-email-haiyangz@microso... Signed-off-by: Wei Liu wei.liu@kernel.org Stable-dep-of: 0315fef2aff9 ("uio_hv_generic: Align ring size to system page") Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/hv/channel_mgmt.c | 96 ++++++++++++++++++++++++++------------- 1 file changed, 64 insertions(+), 32 deletions(-)
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c index 0c6c54061088e..9da36d87ee2c7 100644 --- a/drivers/hv/channel_mgmt.c +++ b/drivers/hv/channel_mgmt.c @@ -579,6 +579,17 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) */ mutex_lock(&vmbus_connection.channel_mutex);
+ list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) { + if (guid_equal(&channel->offermsg.offer.if_type, + &newchannel->offermsg.offer.if_type) && + guid_equal(&channel->offermsg.offer.if_instance, + &newchannel->offermsg.offer.if_instance)) { + fnew = false; + newchannel->primary_channel = channel; + break; + } + } + init_vp_index(newchannel);
/* Remember the channels that should be cleaned up upon suspend. */ @@ -591,16 +602,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) */ atomic_dec(&vmbus_connection.offer_in_progress);
- list_for_each_entry(channel, &vmbus_connection.chn_list, listentry) { - if (guid_equal(&channel->offermsg.offer.if_type, - &newchannel->offermsg.offer.if_type) && - guid_equal(&channel->offermsg.offer.if_instance, - &newchannel->offermsg.offer.if_instance)) { - fnew = false; - break; - } - } - if (fnew) { list_add_tail(&newchannel->listentry, &vmbus_connection.chn_list); @@ -622,7 +623,6 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) /* * Process the sub-channel. */ - newchannel->primary_channel = channel; list_add_tail(&newchannel->sc_list, &channel->sc_list); }
@@ -658,6 +658,30 @@ static void vmbus_process_offer(struct vmbus_channel *newchannel) queue_work(wq, &newchannel->add_channel_work); }
+/* + * Check if CPUs used by other channels of the same device. + * It should only be called by init_vp_index(). + */ +static bool hv_cpuself_used(u32 cpu, struct vmbus_channel *chn) +{ + struct vmbus_channel *primary = chn->primary_channel; + struct vmbus_channel *sc; + + lockdep_assert_held(&vmbus_connection.channel_mutex); + + if (!primary) + return false; + + if (primary->target_cpu == cpu) + return true; + + list_for_each_entry(sc, &primary->sc_list, sc_list) + if (sc != chn && sc->target_cpu == cpu) + return true; + + return false; +} + /* * We use this state to statically distribute the channel interrupt load. */ @@ -677,6 +701,7 @@ static int next_numa_node_id; static void init_vp_index(struct vmbus_channel *channel) { bool perf_chn = hv_is_perf_channel(channel); + u32 i, ncpu = num_online_cpus(); cpumask_var_t available_mask; struct cpumask *alloced_mask; u32 target_cpu; @@ -699,31 +724,38 @@ static void init_vp_index(struct vmbus_channel *channel) return; }
- while (true) { - numa_node = next_numa_node_id++; - if (numa_node == nr_node_ids) { - next_numa_node_id = 0; - continue; + for (i = 1; i <= ncpu + 1; i++) { + while (true) { + numa_node = next_numa_node_id++; + if (numa_node == nr_node_ids) { + next_numa_node_id = 0; + continue; + } + if (cpumask_empty(cpumask_of_node(numa_node))) + continue; + break; } - if (cpumask_empty(cpumask_of_node(numa_node))) - continue; - break; - } - alloced_mask = &hv_context.hv_numa_map[numa_node]; + alloced_mask = &hv_context.hv_numa_map[numa_node];
- if (cpumask_weight(alloced_mask) == - cpumask_weight(cpumask_of_node(numa_node))) { - /* - * We have cycled through all the CPUs in the node; - * reset the alloced map. - */ - cpumask_clear(alloced_mask); - } + if (cpumask_weight(alloced_mask) == + cpumask_weight(cpumask_of_node(numa_node))) { + /* + * We have cycled through all the CPUs in the node; + * reset the alloced map. + */ + cpumask_clear(alloced_mask); + }
- cpumask_xor(available_mask, alloced_mask, cpumask_of_node(numa_node)); + cpumask_xor(available_mask, alloced_mask, + cpumask_of_node(numa_node));
- target_cpu = cpumask_first(available_mask); - cpumask_set_cpu(target_cpu, alloced_mask); + target_cpu = cpumask_first(available_mask); + cpumask_set_cpu(target_cpu, alloced_mask); + + if (channel->offermsg.offer.sub_channel_index >= ncpu || + i > ncpu || !hv_cpuself_used(target_cpu, channel)) + break; + }
channel->target_cpu = target_cpu;