From: Michael Kelley mikelley@microsoft.com
[ Upstream commit 382e06d11e075a40b4094b6ef809f8d4bcc7ab2a ]
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 Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/scsi/storvsc_drv.c | 13 +++++++++++-- 1 file changed, 11 insertions(+), 2 deletions(-)
diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c index d92b2808d191..6df34d68737f 100644 --- a/drivers/scsi/storvsc_drv.c +++ b/drivers/scsi/storvsc_drv.c @@ -641,13 +641,22 @@ static void handle_sc_creation(struct vmbus_channel *new_sc) static void handle_multichannel_storage(struct hv_device *device, int max_chns) { 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;