[Stgt-devel] [PATCH] iscsi tcp: optimize rx

[FUJITA Tomonori]

From: Pete Wyckoff <pw at osc.edu>
Subject: [Stgt-devel] [PATCH] iscsi tcp: optimize rx
Date: Sat, 29 Dec 2007 14:01:58 -0500

> Avoid another trip through the event loop in the case of an
> RX with no AHS, by jumping up to the top of the state machine
> directly.  This saves about 500 ns per command on my hardware.
> 
> Signed-off-by: Pete Wyckoff <pw at osc.edu>
> ---
>  usr/iscsi/iscsid.c |    4 +++-
>  1 files changed, 3 insertions(+), 1 deletions(-)
> 
> diff --git a/usr/iscsi/iscsid.c b/usr/iscsi/iscsid.c
> index 8872818..bbab32d 100644
> --- a/usr/iscsi/iscsid.c
> +++ b/usr/iscsi/iscsid.c
> @@ -1845,9 +1845,11 @@ again:
>  		if (conn->rx_size) {
>  			conn->rx_buffer = conn->req.ahs;
>  			conn->rx_iostate = IOSTATE_RX_AHS;
> -		} else
> +		} else {
>  			conn->rx_iostate = hdigest ?
>  				IOSTATE_RX_INIT_HDIGEST : IOSTATE_RX_INIT_DATA;
> +			goto again;
> +		}
>  
>  		/*
>  		 * if the datasize is zero, we must go to

Hmm, here we have:

		if (conn->rx_iostate == IOSTATE_RX_INIT_DATA)
			goto again;
		else if (conn->rx_iostate != IOSTATE_RX_AHS)
			break;

conn->rx_iostate == IOSTATE_RX_INIT_DATA case already goes to again?
What case do you try to improve?