diff options
| author | Michael Kelley <mikelley@microsoft.com> | 2019-04-01 16:10:52 +0000 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-05-08 07:19:10 +0200 |
| commit | 9cdaf16efabddb9a839157a1a4b7a716b1e38978 (patch) | |
| tree | 8cdd9687d31bf3bfbf53f29a934bdeee0d35cc3d /drivers/scsi/storvsc_drv.c | |
| parent | 7a4973dd1ca199a7c091c6c081089c305e353afc (diff) | |
scsi: storvsc: Fix calculation of sub-channel count
[ 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>
Diffstat (limited to 'drivers/scsi/storvsc_drv.c')
| -rw-r--r-- | drivers/scsi/storvsc_drv.c | 13 |
1 files 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; |