From: Dexuan Cui <decui@microsoft.com>
To: Vitaly Kuznetsov <vkuznets@redhat.com>, KY Srinivasan <kys@microsoft.com>
CC: Haiyang Zhang <haiyangz@microsoft.com>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH v2 0/6] Drivers: hv: vmbus: fair round robin algorithm for
 vmbus_get_outgoing_channel()
Thread-Topic: [PATCH v2 0/6] Drivers: hv: vmbus: fair round robin algorithm
 for vmbus_get_outgoing_channel()
Thread-Index: AQHQgQw5zzR6yZqoq0K9SCTs74Pt0p1h1KDw
Date: Tue, 28 Apr 2015 04:30:13 +0000
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> -----Original Message-----
> From: Vitaly Kuznetsov [mailto:vkuznets@redhat.com]
> Sent: Tuesday, April 28, 2015 1:04
> To: KY Srinivasan
> Cc: Haiyang Zhang; devel@linuxdriverproject.org; linux-
> kernel@vger.kernel.org; Dexuan Cui
> Subject: [PATCH v2 0/6] Drivers: hv: vmbus: fair round robin algorithm for
> vmbus_get_outgoing_channel()
> 
> Changes in v2:
> - Address Dexuan's review comments:
>   PATCH 3/6: s,channel,primary_channel;
>   PATCH 4/6: add a forward declaration instead of moving code around;
>   PATCH 6/6: fix an off-by-one
> - Change the algorithm in PATCH 6/6:
>   Instead of a simple round robin we first try to find a (sub)channel with
>   the current_cpu == target_cpu and we fallback to a round robin when we
> fail
>   to find one.
> 
> K. Y., Dexuan, can you please give it a spin in various testing environments
> you have? Thanks!
> 
> Original description:
> 
> This series is a continuation of the "Drivers: hv: vmbus: Use a round-robin
> algorithm for picking the outgoing channel" work. It is supposed to bring
> two
> significant changes:
> 1) Subchannels for a channel are distributed evenly across all vcpus we have.
>    Currently we try to distribute all channels (including subchannels) across
>    all vcpus, this approach doesn't guarantee that the particular channel's
>    subchannels will be distributed in the same way as we process all offer
>    requests in some random order. (Patch 05)
> 2) Channel picking based on the current vcpu is dropped from
>    vmbus_get_outgoing_channel() in favor of a fair round robin. (Patch 06)
> (this
>    is not true anymore, see 'Changes').
> 
> Patches 01 - 04 are cleanup/refactoring.
> 
> Vitaly Kuznetsov (6):
>   Drivers: hv: vmbus: unify calls to percpu_channel_enq()
>   Drivers: hv: vmbus: briefly comment num_sc and next_oc
>   Drivers: hv: vmbus: decrease num_sc on subchannel removal
>   Drivers: hv: vmbus: move init_vp_index() call to vmbus_process_offer()
>   Drivers: hv: vmbus: distribute subchannels among all vcpus
>   Drivers: hv: vmbus: improve selection of an outgoing channel
> 
>  drivers/hv/channel_mgmt.c | 127 ++++++++++++++++++++++++++---------
> -----------
>  include/linux/hyperv.h    |  12 +++--
>  2 files changed, 80 insertions(+), 59 deletions(-)
> 
> --

Patch 1, 2 and 3 are good to me.

We'll have to test 4~6 for performance change.

Thanks,
-- Dexuan
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