• Zhang Yanmin's avatar
    [NET]: Fix tbench regression in 2.6.25-rc1 · f1dd9c37
    Zhang Yanmin authored
    Comparing with kernel 2.6.24, tbench result has regression with
    2.6.25-rc1.
    
    1) On 2 quad-core processor stoakley: 4%.
    2) On 4 quad-core processor tigerton: more than 30%.
    
    bisect located below patch.
    
    b4ce9277 is first bad commit
    commit b4ce9277
    
    
    Author: Herbert Xu <herbert@gondor.apana.org.au>
    Date:   Tue Nov 13 21:33:32 2007 -0800
    
        [IPV6]: Move nfheader_len into rt6_info
    
        The dst member nfheader_len is only used by IPv6.  It's also currently
        creating a rather ugly alignment hole in struct dst.  Therefore this patch
        moves it from there into struct rt6_info.
    
    Above patch changes the cache line alignment, especially member
    __refcnt. I did a testing by adding 2 unsigned long pading before
    lastuse, so the 3 members, lastuse/__refcnt/__use, are moved to next
    cache line. The performance is recovered.
    
    I created a patch to rearrange the members in struct dst_entry.
    
    With Eric and Valdis Kletnieks's suggestion, I made finer arrangement.
    
    1) Move tclassid under ops in case CONFIG_NET_CLS_ROUTE=y. So
       sizeof(dst_entry)=200 no matter if CONFIG_NET_CLS_ROUTE=y/n. I
       tested many patches on my 16-core tigerton by moving tclassid to
       different place. It looks like tclassid could also have impact on
       performance.  If moving tclassid before metrics, or just don't move
       tclassid, the performance isn't good. So I move it behind metrics.
    
    2) Add comments before __refcnt.
    
    On 16-core tigerton:
    
    If CONFIG_NET_CLS_ROUTE=y, the result with below patch is about 18%
    better than the one without the patch;
    
    If CONFIG_NET_CLS_ROUTE=n, the result with below patch is about 30%
    better than the one without the patch.
    
    With 32bit 2.6.25-rc1 on 8-core stoakley, the new patch doesn't
    introduce regression.
    
    Thank Eric, Valdis, and David!
    Signed-off-by: default avatarZhang Yanmin <yanmin.zhang@intel.com>
    Acked-by: default avatarEric Dumazet <dada1@cosmosbay.com>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    f1dd9c37