Subject: Re: [RFC PATCH v3 3/7] proc: Reduce cache miss in snmp6_seq_show

From: Marcelo <[email-masked]>
Date: Mon, 12 Sep 2016 16:05:02 -0300

On Fri, Sep 09, 2016 at 02:33:58PM +0800, Jia He wrote:
> This is to use the generic interface snmp_get_cpu_field{,64}_batch to 
> aggregate the data by going through all the items of each cpu sequentially.
> 
> Signed-off-by: Jia He <[email-masked]>
> ---
>  net/ipv6/proc.c | 32 +++++++++++++++++++++++---------
>  1 file changed, 23 insertions(+), 9 deletions(-)
> 
> diff --git a/net/ipv6/proc.c b/net/ipv6/proc.c
> index 679253d0..50ba2c3 100644
> --- a/net/ipv6/proc.c
> +++ b/net/ipv6/proc.c
> @@ -30,6 +30,11 @@
>  #include <net/transp_v6.h>
>  #include <net/ipv6.h>
>  
> +#define MAX4(a, b, c, d) \
> +	max_t(u32, max_t(u32, a, b), max_t(u32, c, d))
> +#define SNMP_MIB_MAX MAX4(UDP_MIB_MAX, TCP_MIB_MAX, \
> +			IPSTATS_MIB_MAX, ICMP_MIB_MAX)
> +
>  static int sockstat6_seq_show(struct seq_file *seq, void *v)
>  {
>  	struct net *net = seq->private;
> @@ -192,13 +197,19 @@ static void snmp6_seq_show_item(struct seq_file *seq, void __percpu *pcpumib,
>  				const struct snmp_mib *itemlist)
>  {
>  	int i;
> -	unsigned long val;
> -
> -	for (i = 0; itemlist[i].name; i++) {
> -		val = pcpumib ?
> -			snmp_fold_field(pcpumib, itemlist[i].entry) :
> -			atomic_long_read(smib + itemlist[i].entry);
> -		seq_printf(seq, "%-32s\t%lu\n", itemlist[i].name, val);
> +	unsigned long buff[SNMP_MIB_MAX];
> +
> +	memset(buff, 0, sizeof(unsigned long) * SNMP_MIB_MAX);

This memset() could be moved...

> +
> +	if (pcpumib) {

... here, so it's not executed if it hits the else block.

> +		snmp_get_cpu_field_batch(buff, itemlist, pcpumib);
> +		for (i = 0; itemlist[i].name; i++)
> +			seq_printf(seq, "%-32s\t%lu\n",
> +				   itemlist[i].name, buff[i]);
> +	} else {
> +		for (i = 0; itemlist[i].name; i++)
> +			seq_printf(seq, "%-32s\t%lu\n", itemlist[i].name,
> +				   atomic_long_read(smib + itemlist[i].entry));
>  	}
>  }
>  
> @@ -206,10 +217,13 @@ static void snmp6_seq_show_item64(struct seq_file *seq, void __percpu *mib,
>  				  const struct snmp_mib *itemlist, size_t syncpoff)
>  {
>  	int i;
> +	u64 buff64[SNMP_MIB_MAX];
> +
> +	memset(buff64, 0, sizeof(unsigned long) * SNMP_MIB_MAX);
>  
> +	snmp_get_cpu_field64_batch(buff64, itemlist, mib, syncpoff);
>  	for (i = 0; itemlist[i].name; i++)
> -		seq_printf(seq, "%-32s\t%llu\n", itemlist[i].name,
> -			   snmp_fold_field64(mib, itemlist[i].entry, syncpoff));
> +		seq_printf(seq, "%-32s\t%llu\n", itemlist[i].name, buff64[i]);
>  }
>  
>  static int snmp6_seq_show(struct seq_file *seq, void *v)
> -- 
> 1.8.3.1
> 
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