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Subject[PATCH 5/6] Drivers: hv: vmbus: distribute subchannels among all vcpus
Date
Primary channels are distributed evenly across all vcpus we have. When the host
asks us to create subchannels it usually makes us num_cpus-1 offers and we are
supposed to distribute the work evenly among the channel itself and all its
subchannels. Make sure they are all assigned to different vcpus.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
---
drivers/hv/channel_mgmt.c | 29 ++++++++++++++++++++++++++++-
1 file changed, 28 insertions(+), 1 deletion(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 8f2761f..daa6417 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -270,6 +270,8 @@ static void init_vp_index(struct vmbus_channel *channel,
int i;
bool perf_chn = false;
u32 max_cpus = num_online_cpus();
+ struct vmbus_channel *primary = channel->primary_channel, *prev;
+ unsigned long flags;

for (i = IDE; i < MAX_PERF_CHN; i++) {
if (!memcmp(type_guid->b, hp_devs[i].guid,
@@ -290,7 +292,32 @@ static void init_vp_index(struct vmbus_channel *channel,
channel->target_vp = 0;
return;
}
- cur_cpu = (++next_vp % max_cpus);
+
+ /*
+ * Primary channels are distributed evenly across all vcpus we have.
+ * When the host asks us to create subchannels it usually makes us
+ * num_cpus-1 offers and we are supposed to distribute the work evenly
+ * among the channel itself and all its subchannels. Make sure they are
+ * all assigned to different vcpus.
+ */
+ if (!primary)
+ cur_cpu = (++next_vp % max_cpus);
+ else {
+ /*
+ * Let's assign the first subchannel of a channel to the
+ * primary->target_cpu+1 and all the subsequent channels to
+ * the prev->target_cpu+1.
+ */
+ spin_lock_irqsave(&primary->lock, flags);
+ if (primary->num_sc == 1)
+ cur_cpu = (primary->target_cpu + 1) % max_cpus;
+ else {
+ prev = list_prev_entry(channel, sc_list);
+ cur_cpu = (prev->target_cpu + 1) % max_cpus;
+ }
+ spin_unlock_irqrestore(&primary->lock, flags);
+ }
+
channel->target_cpu = cur_cpu;
channel->target_vp = hv_context.vp_index[cur_cpu];
}
--
1.9.3


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