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@xxxxxxxxxxxxx>
Reviewed-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
Changes in v2:
* Put num_online_cpus() inline and eliminate num_cpus local
variable [Vitaly Kuznetsov]
---
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 84380ba..e186743 100644
--- a/drivers/scsi/storvsc_drv.c
+++ b/drivers/scsi/storvsc_drv.c
@@ -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;
--
1.8.3.1
