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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@microsoft.com Signed-off-by: Wei Liu <wei.liu@kernel.org> |
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.. | ||
channel_mgmt.c | ||
channel.c | ||
connection.c | ||
hv_balloon.c | ||
hv_common.c | ||
hv_debugfs.c | ||
hv_fcopy.c | ||
hv_kvp.c | ||
hv_snapshot.c | ||
hv_trace_balloon.h | ||
hv_trace.c | ||
hv_trace.h | ||
hv_util.c | ||
hv_utils_transport.c | ||
hv_utils_transport.h | ||
hv.c | ||
hyperv_vmbus.h | ||
Kconfig | ||
Makefile | ||
ring_buffer.c | ||
vmbus_drv.c |