| Message ID | 1554076559-14873-1-git-send-email-mikelley@microsoft.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | [1/1] scsi: storvsc: Fix calculation of sub-channel count | expand |
Michael Kelley <mikelley@microsoft.com> writes: > 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> > --- > drivers/scsi/storvsc_drv.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c > index 84380ba..fbaa11a 100644 > --- a/drivers/scsi/storvsc_drv.c > +++ b/drivers/scsi/storvsc_drv.c > @@ -674,7 +674,17 @@ static void handle_multichannel_storage(struct hv_device *device, int max_chns) > 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. > + */ Indeed. > + num_sc = min((num_cpus - 1), max_chns); Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> (nit: you could've written num_sc = min((num_online_cpus() - 1), max_chns); and got rid of the now-unneeded num_cpus variable). > + if (!num_sc) > + return; > + > stor_device = get_out_stor_device(device); > if (!stor_device) > return;
diff --git a/drivers/scsi/storvsc_drv.c b/drivers/scsi/storvsc_drv.c index 84380ba..fbaa11a 100644 --- a/drivers/scsi/storvsc_drv.c +++ b/drivers/scsi/storvsc_drv.c @@ -674,7 +674,17 @@ static void handle_multichannel_storage(struct hv_device *device, int max_chns) 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((num_cpus - 1), max_chns); + if (!num_sc) + return; + stor_device = get_out_stor_device(device); if (!stor_device) return;
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> --- drivers/scsi/storvsc_drv.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-)