Commit 382e06d1 authored Apr 01, 2019 by Michael Kelley Committed by Martin K. Petersen Apr 03, 2019

scsi: storvsc: Fix calculation of sub-channel count



When the number of sub-channels offered by Hyper-V is >= the number of CPUs
in the VM, calculate the correct number of sub-channels.  The current code
produces one too many.

This scenario arises only when the number of CPUs is artificially
restricted (for example, with maxcpus=<n> on the kernel boot line), because
Hyper-V normally offers a sub-channel count < number of CPUs.  While the
current code doesn't break, the extra sub-channel is unbalanced across the
CPUs (for example, a total of 5 channels on a VM with 4 CPUs).

Signed-off-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Reviewed-by: Long Li <longli@microsoft.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

parent 1cb1d2c6

drivers/scsi/storvsc_drv.c

+11 −2

Original line number	Diff line number	Diff line
		@@ -668,13 +668,22 @@ static void handle_multichannel_storage(struct hv_device *device, int max_chns)
		{
		struct device *dev = &device->device;
		struct storvsc_device *stor_device;
		int num_cpus = num_online_cpus();
		int num_sc;
		struct storvsc_cmd_request *request;
		struct vstor_packet *vstor_packet;
		int ret, t;

		num_sc = ((max_chns > num_cpus) ? num_cpus : max_chns);
		/*
		* If the number of CPUs is artificially restricted, such as
		* with maxcpus=1 on the kernel boot line, Hyper-V could offer
		* sub-channels >= the number of CPUs. These sub-channels
		* should not be created. The primary channel is already created
		* and assigned to one CPU, so check against # CPUs - 1.
		*/
		num_sc = min((int)(num_online_cpus() - 1), max_chns);
		if (!num_sc)
		return;

		stor_device = get_out_stor_device(device);
		if (!stor_device)
		return;

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