netdev - RE: [PATCH net] hvsock: fix epollout hang from race condition

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Message-ID: <PU1P153MB016994A9A0C4C3D1306B8FE4BFEF0@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>
Date:   Thu, 13 Jun 2019 23:35:53 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Sunil Muthuswamy <sunilmut@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Michael Kelley <mikelley@...rosoft.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH net] hvsock: fix epollout hang from race condition

> From: Sunil Muthuswamy <sunilmut@...rosoft.com>
> Sent: Wednesday, June 12, 2019 2:19 PM
>  ...
> The fix is to set the pending size to the default size and never change it.
> This way the host will always notify the guest whenever the writable space
> is bigger than the pending size. The host is already optimized to *only*
> notify the guest when the pending size threshold boundary is crossed and
> not everytime.
> 
> This change also reduces the cpu usage somewhat since
> hv_stream_has_space()
> is in the hotpath of send:
> vsock_stream_sendmsg()->hv_stream_has_space()
> Earlier hv_stream_has_space was setting/clearing the pending size on every
> call.
> 
> Signed-off-by: Sunil Muthuswamy <sunilmut@...rosoft.com>

Hi Sunil, thanks for the fix! It looks good.

Reviewed-by: Dexuan Cui <decui@...rosoft.com>