Re: [PATCH v2 07/12] icmp: Simplify socket expiry scanning

[Stefano Brivio <sbrivio@redhat.com>]

On Thu, 21 Dec 2023 17:53:22 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:

> Currently we use icmp_act[] to scan for ICMP ids which might have an open
> socket which could time out.  However icmp_act[] contains no information
> that's not already in icmp_id_map[] - it's just an "index" which allows
> scanning for relevant entries with less cache footprint.
> 
> We only scan for ICMP socket expiry every 1s, though, so it's not clear
> that cache footprint really matters.  Furthermore, there's no strong reason
> we need to scan even that often - the timeout is fairly arbitrary and
> approximate.
> 
> So, eliminate icmp_act[] in favour of directly scanning icmp_id_map[] and
> compensate for the cache impact by reducing the scan frequency to once
> every 10s.
> 
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
>  icmp.c | 34 ++++++----------------------------
>  icmp.h |  2 +-
>  2 files changed, 7 insertions(+), 29 deletions(-)
> 
> diff --git a/icmp.c b/icmp.c
> index dd98c7f..02739b9 100644
> --- a/icmp.c
> +++ b/icmp.c
> @@ -56,9 +56,6 @@ struct icmp_id_sock {
>  /* Indexed by ICMP echo identifier */
>  static struct icmp_id_sock icmp_id_map[IP_VERSIONS][ICMP_NUM_IDS];
>  
> -/* Bitmaps, activity monitoring needed for identifier */
> -static uint8_t icmp_act[IP_VERSIONS][DIV_ROUND_UP(ICMP_NUM_IDS, 8)];
> -
>  /**
>   * icmp_sock_handler() - Handle new data from IPv4 ICMP socket
>   * @c:		Execution context
> @@ -194,7 +191,6 @@ int icmp_tap_handler(const struct ctx *c, uint8_t pif, int af,
>  			debug("ICMP: new socket %i for echo ID %i", s, id);
>  		}
>  		icmp_id_map[V4][id].ts = now->tv_sec;
> -		bitmap_set(icmp_act[V4], id);
>  
>  		sa.sin_addr = *(struct in_addr *)daddr;
>  		if (sendto(s, ih, sizeof(*ih) + plen, MSG_NOSIGNAL,
> @@ -237,7 +233,6 @@ int icmp_tap_handler(const struct ctx *c, uint8_t pif, int af,
>  			debug("ICMPv6: new socket %i for echo ID %i", s, id);
>  		}
>  		icmp_id_map[V6][id].ts = now->tv_sec;
> -		bitmap_set(icmp_act[V6], id);
>  
>  		sa.sin6_addr = *(struct in6_addr *)daddr;
>  		if (sendto(s, ih, sizeof(*ih) + plen, MSG_NOSIGNAL,
> @@ -261,20 +256,15 @@ fail_sock:
>  /**
>   * icmp_timer_one() - Handler for timed events related to a given identifier
>   * @c:		Execution context
> - * @v6:		Set for IPv6 echo identifier bindings
> - * @id:		Echo identifier, host order
> + * @id_map:	id socket information to check timers for

It took me a few readings to understand this... what about:

 * @id_sock:	Socket number and activity timestamp

?

-- 
Stefano