linux-kernel - Re: [RFC PATCH v5 2/2] virtio/vsock: check argument to avoid no effect call

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Message-ID: <20230323092905.fpsiiaca2ba2wug3@sgarzare-redhat>
Date:   Thu, 23 Mar 2023 10:29:05 +0100
From:   Stefano Garzarella <sgarzare@...hat.com>
To:     Arseniy Krasnov <avkrasnov@...rdevices.ru>
Cc:     Stefan Hajnoczi <stefanha@...hat.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Bobby Eshleman <bobby.eshleman@...edance.com>,
        kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel@...rdevices.ru, oxffffaa@...il.com
Subject: Re: [RFC PATCH v5 2/2] virtio/vsock: check argument to avoid no
 effect call

On Wed, Mar 22, 2023 at 09:36:24PM +0300, Arseniy Krasnov wrote:
>Both of these functions have no effect when input argument is 0, so to
>avoid useless spinlock access, check argument before it.
>
>Signed-off-by: Arseniy Krasnov <AVKrasnov@...rdevices.ru>
>---
> net/vmw_vsock/virtio_transport_common.c | 6 ++++++
> 1 file changed, 6 insertions(+)

Reviewed-by: Stefano Garzarella <sgarzare@...hat.com>

>
>diff --git a/net/vmw_vsock/virtio_transport_common.c b/net/vmw_vsock/virtio_transport_common.c
>index 9e87c7d4d7cf..312658c176bd 100644
>--- a/net/vmw_vsock/virtio_transport_common.c
>+++ b/net/vmw_vsock/virtio_transport_common.c
>@@ -302,6 +302,9 @@ u32 virtio_transport_get_credit(struct virtio_vsock_sock *vvs, u32 credit)
> {
> 	u32 ret;
>
>+	if (!credit)
>+		return 0;
>+
> 	spin_lock_bh(&vvs->tx_lock);
> 	ret = vvs->peer_buf_alloc - (vvs->tx_cnt - vvs->peer_fwd_cnt);
> 	if (ret > credit)
>@@ -315,6 +318,9 @@ EXPORT_SYMBOL_GPL(virtio_transport_get_credit);
>
> void virtio_transport_put_credit(struct virtio_vsock_sock *vvs, u32 credit)
> {
>+	if (!credit)
>+		return;
>+
> 	spin_lock_bh(&vvs->tx_lock);
> 	vvs->tx_cnt -= credit;
> 	spin_unlock_bh(&vvs->tx_lock);
>-- 
>2.25.1
>