netdev - Re: [RFC PATCH v2 1/9] vsock: use sk_rcvlowat to set POLLIN/POLLRDNORM

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Message-ID: <20220727121709.z26dspwegqeiv55x@sgarzare-redhat>
Date:   Wed, 27 Jul 2022 14:17:09 +0200
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <AVKrasnov@...rdevices.ru>
Cc:     "David S. Miller" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "kys@...rosoft.com" <kys@...rosoft.com>,
        "haiyangz@...rosoft.com" <haiyangz@...rosoft.com>,
        "sthemmin@...rosoft.com" <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Dexuan Cui <decui@...rosoft.com>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Krasnov Arseniy <oxffffaa@...il.com>,
        "virtualization@...ts.linux-foundation.org" 
        <virtualization@...ts.linux-foundation.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        kernel <kernel@...rdevices.ru>
Subject: Re: [RFC PATCH v2 1/9] vsock: use sk_rcvlowat to set
 POLLIN/POLLRDNORM

On Mon, Jul 25, 2022 at 07:56:59AM +0000, Arseniy Krasnov wrote:
>Both bits indicate, that next data read call won't be blocked, but when
>sk_rcvlowat is not 1, these bits will be set by poll anyway, thus when
>user tries to dequeue data,it will wait until sk_rcvlowat bytes of data
>will be available.
>

The patch LGTM, but I suggest you to rewrite the title and commit of the 
message to better explain what this patch does (pass sock_rcvlowat to 
notify_poll_in as target) and then explain why as you already did (to 
set POLLIN/POLLRDNORM only when target is reached).

Thanks,
Stefano

>Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
>---
> net/vmw_vsock/af_vsock.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
>diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
>index f04abf662ec6..63a13fa2686a 100644
>--- a/net/vmw_vsock/af_vsock.c
>+++ b/net/vmw_vsock/af_vsock.c
>@@ -1066,8 +1066,9 @@ static __poll_t vsock_poll(struct file *file, struct socket *sock,
> 		if (transport && transport->stream_is_active(vsk) &&
> 		    !(sk->sk_shutdown & RCV_SHUTDOWN)) {
> 			bool data_ready_now = false;
>+			int target = sock_rcvlowat(sk, 0, INT_MAX);
> 			int ret = transport->notify_poll_in(
>-					vsk, 1, &data_ready_now);
>+					vsk, target, &data_ready_now);
> 			if (ret < 0) {
> 				mask |= EPOLLERR;
> 			} else {
>-- 
>2.25.1