vmbus_get_outgoing_channel() implements the following algorithm for selecting
an outgoing channel (despite the comment before the function saying it
distributes the load equally):
1) If we have no subchannels return the primary channel;
2) If primary->next_oc is grater than primary->num_sc reset the primary->next_oc
to 0 and return the primary channel;
3) Aim for the primary->next_oc subchannel, increment primary->next_oc;
4) Loop through all opened subchannels. If we see a channel which has
target_cpu == current_cpu return it. If we reached the primary->next_oc'th
open subchannel return it;
5) Return the primary channel.
The implementation also skips the subchannel No. 0 unless it matches the current
cpu as we assign i to 1 in the initialization.
Improve the algorithm to do the full scan searching for a (sub)channel with the
target_cpu == current_cpu, use round-robin as a fallback.
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
drivers/hv/channel_mgmt.c | 39 +++++++++++++++++++--------------------
1 file changed, 19 insertions(+), 20 deletions(-)
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 1f1417d..cdc3914 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -823,46 +823,45 @@ cleanup:
}
/*
- * Retrieve the (sub) channel on which to send an outgoing request.
- * When a primary channel has multiple sub-channels, we try to
- * distribute the load equally amongst all available channels.
+ * Retrieve the (sub) channel on which to send an outgoing request. When a
+ * primary channel has multiple sub-channels, we try to find a (sub)channel
+ * with target_cpu == current CPU and we try to distribute the load equally
+ * amongst all available channels when we fail.
*/
struct vmbus_channel *vmbus_get_outgoing_channel(struct vmbus_channel *primary)
{
struct list_head *cur, *tmp;
- int cur_cpu;
struct vmbus_channel *cur_channel;
- struct vmbus_channel *outgoing_channel = primary;
- int next_channel;
- int i = 1;
+ struct vmbus_channel *out_channel_rr = NULL;
+ int i = 0;
if (list_empty(&primary->sc_list))
- return outgoing_channel;
+ return primary;
- next_channel = primary->next_oc++;
-
- if (next_channel > (primary->num_sc)) {
+ if (primary->next_oc >= primary->num_sc) {
primary->next_oc = 0;
- return outgoing_channel;
+ return primary;
}
- cur_cpu = hv_context.vp_index[get_cpu()];
- put_cpu();
+ if (primary->target_cpu == smp_processor_id())
+ return primary;
+
list_for_each_safe(cur, tmp, &primary->sc_list) {
+ i++;
cur_channel = list_entry(cur, struct vmbus_channel, sc_list);
if (cur_channel->state != CHANNEL_OPENED_STATE)
continue;
- if (cur_channel->target_vp == cur_cpu)
+ if (cur_channel->target_cpu == smp_processor_id())
return cur_channel;
- if (i == next_channel)
- return cur_channel;
-
- i++;
+ if (!out_channel_rr && i > primary->next_oc) {
+ primary->next_oc = i;
+ out_channel_rr = cur_channel;
+ }
}
- return outgoing_channel;
+ return out_channel_rr ? out_channel_rr : primary;
}
EXPORT_SYMBOL_GPL(vmbus_get_outgoing_channel);
--
1.9.3
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