size calculation wasted cpu time

size calculation wasted cpu time

[Kuzin Andrey]

In /net/netfilter/nfnetlink_queue.c every call of nfqnl_build_packet_message()
make series of call nla_total_size() for 'size' calculations.
I think 'size' is constant value for kernel build and may be define static
variable for this ?

Thank you.

static struct sk_buff *
nfqnl_build_packet_message(struct nfqnl_instance *queue,
                           struct nf_queue_entry *entry)
{
        sk_buff_data_t old_tail;
        size_t size;
        size_t data_len = 0;
        struct sk_buff *skb;
        struct nfqnl_msg_packet_hdr pmsg;
        struct nlmsghdr *nlh;
        struct nfgenmsg *nfmsg;
        struct sk_buff *entskb = entry->skb;
        struct net_device *indev;
        struct net_device *outdev;

        size =    NLMSG_SPACE(sizeof(struct nfgenmsg))
                + nla_total_size(sizeof(struct nfqnl_msg_packet_hdr))
                + nla_total_size(sizeof(u_int32_t))     /* ifindex */
                + nla_total_size(sizeof(u_int32_t))     /* ifindex */
#ifdef CONFIG_BRIDGE_NETFILTER
                + nla_total_size(sizeof(u_int32_t))     /* ifindex */
                + nla_total_size(sizeof(u_int32_t))     /* ifindex */
#endif
                + nla_total_size(sizeof(u_int32_t))     /* mark */
                + nla_total_size(sizeof(struct nfqnl_msg_packet_hw))
                + nla_total_size(sizeof(struct nfqnl_msg_packet_timestamp));

Re: size calculation wasted cpu time

[Pablo Neira Ayuso]

Kuzin Andrey wrote:
> In /net/netfilter/nfnetlink_queue.c every call of nfqnl_build_packet_message()
> make series of call nla_total_size() for 'size' calculations.
> I think 'size' is constant value for kernel build and may be define static
> variable for this ?

We can calculate this during the module initialization, brave to cook a
patch for it?

-- 
"Los honestos son inadaptados sociales" -- Les Luthiers

Re: size calculation wasted cpu time

[Patrick McHardy]

Pablo Neira Ayuso wrote:
> Kuzin Andrey wrote:
>> In /net/netfilter/nfnetlink_queue.c every call of nfqnl_build_packet_message()
>> make series of call nla_total_size() for 'size' calculations.
>> I think 'size' is constant value for kernel build and may be define static
>> variable for this ?
> 
> We can calculate this during the module initialization, brave to cook a
> patch for it?

The compiler should realize its constant and perform the calculation
at calculation time.

Re: size calculation wasted cpu time

[Jan Engelhardt]

On Monday 2009-03-16 14:02, Kuzin Andrey wrote:

>In /net/netfilter/nfnetlink_queue.c every call of nfqnl_build_packet_message()
>make series of call nla_total_size() for 'size' calculations.
>I think 'size' is constant value for kernel build and may be define static
>variable for this ?
>
>        size =    NLMSG_SPACE(sizeof(struct nfgenmsg))
>                + nla_total_size(sizeof(struct nfqnl_msg_packet_hdr))
>                + nla_total_size(sizeof(u_int32_t))     /* ifindex */
>                + nla_total_size(sizeof(u_int32_t))     /* ifindex */

The compiler will optimize it out.

Re[2]: size calculation wasted cpu time

[Kuzin Andrey]

>>In /net/netfilter/nfnetlink_queue.c every call of nfqnl_build_packet_message()
>>make series of call nla_total_size() for 'size' calculations.
>>I think 'size' is constant value for kernel build and may be define static
>>variable for this ?
>>
>>        size =    NLMSG_SPACE(sizeof(struct nfgenmsg))
>>                + nla_total_size(sizeof(struct nfqnl_msg_packet_hdr))
>>                + nla_total_size(sizeof(u_int32_t))     /* ifindex */
>>                + nla_total_size(sizeof(u_int32_t))     /* ifindex */

JE> The compiler will optimize it out.

Okey. It's easy to test.


=========== 1.c =======================

#include <stdlib.h>
#include <stdio.h>
#define NLA_ALIGNTO             4
#define NLA_ALIGN(len)          (((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1))
#define NLA_HDRLEN              30

static inline int nla_attr_size(int payload)
{
      return NLA_HDRLEN + payload;
}

static inline int nla_total_size(int payload)
{
      return NLA_ALIGN(nla_attr_size(payload));
}

size_t nfqnl_build_packet_message(int len) {
      size_t size;

      size = nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t));     /* mark */

      return size;
};


int main () {
      long i;
      size_t ret;

      int r = 0;
      for (i = 0; i < 100000000; i++) {
            r = rand();
            printf("%d",r);
            ret = nfqnl_build_packet_message(r);
      };
}
======================== end of 1.c ========================

And other case

===================== 2.c =============================

#include <stdlib.h>
#include <stdio.h>

#define NLA_ALIGNTO             4
#define NLA_ALIGN(len)          (((len) + NLA_ALIGNTO - 1) & ~(NLA_ALIGNTO - 1))
#define NLA_HDRLEN              30

static inline int nla_attr_size(int payload)
{
      return NLA_HDRLEN + payload;
}

static inline int nla_total_size(int payload)
{
      return NLA_ALIGN(nla_attr_size(payload));
}

size_t size_global = 0; ///// GLOBAL PRECALCULATED VALUE

size_t nfqnl_build_packet_message(int len) {
      size_t size;

      size = size_global;

      return size;
};


int main () {
      long i;
      size_t ret;

      //////// calculations here
      size_global = nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t))     /* ifindex */
            + nla_total_size(sizeof(u_int32_t));     /* mark */

      int r = 0;
      for (i = 0; i < 100000000; i++) {
            r = rand();
            printf("%d",r);
            ret = nfqnl_build_packet_message(r);
      };
}
===========================================

And some tests....


root@bill:/src/1# gcc 1.c
root@bill:/src/1# time ./a.out > /dev/null
real    0m20.253s
user    0m20.209s
sys     0m0.041s

root@bill:/src/1# gcc 2.c
root@bill:/src/1# time ./a.out > /dev/null
real    0m17.030s
user    0m16.988s
sys     0m0.040s

=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Kuzin Andrey  -  kuzinandrey@yandex.ru
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=

Re: Re[2]: size calculation wasted cpu time

[Henrik Nordstrom]

lör 2009-07-25 klockan 09:10 +0400 skrev Kuzin Andrey:

> root@bill:/src/1# gcc 1.c

Now try the same with -O2

Regards
Henrik

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