| Message ID | 1554134985-8671-1-git-send-email-mikelley@microsoft.com (mailing list archive) |
|---|---|
| State | Mainlined |
| Commit | 382e06d11e075a40b4094b6ef809f8d4bcc7ab2a |
| Headers | show |
| Series | [v2,1/1] scsi: storvsc: Fix calculation of sub-channel count | expand |
>>>-----Original Message----- >>>From: Michael Kelley <mikelley@microsoft.com> >>>Sent: Monday, April 1, 2019 9:11 AM >>>To: KY Srinivasan <kys@microsoft.com>; martin.petersen@oracle.com; Long >>>Li <longli@microsoft.com>; James.Bottomley@hansenpartnership.com; >>>emilne@redhat.com; linux-hyperv@vger.kernel.org; linux- >>>kernel@vger.kernel.org; linux-scsi@vger.kernel.org >>>Cc: Michael Kelley <mikelley@microsoft.com> >>>Subject: [PATCH v2 1/1] 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> >>>--- >>>Changes in v2: >>>* Put num_online_cpus() inline and eliminate num_cpus local >>> variable [Vitaly Kuznetsov] >>> Reviewed-by: Long Li <longli@microsoft.com> >>>--- >>> 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
Michael, > 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. Applied to 5.1/scsi-fixes, thanks.
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;