lkml.org 
[lkml]   [2006]   [Jan]   [30]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [PATCH 1/5] pid: Implement task references.
    From
    Date
    Eric Dumazet <dada1@cosmosbay.com> writes:

    > This function is not inlined.
    >
    > Adding a test and a branch is a matter of 7 bytes.
    >
    > 'Bloating the icache' is a litle bit off :)

    The size all depends on your architecture. But I agree it
    is not much of a size increase in general.

    > Avoiding an atomic is important. This is already done elsewhere in the kernel,
    > in a inlined function with *many* call sites :
    >
    > (See kfree_skb() in include/linux//skbuff.h )
    >
    > /*
    > * If users == 1, we are the only owner and are can avoid redundant
    > * atomic change.
    > */
    >
    > /**
    > * kfree_skb - free an sk_buff
    > * @skb: buffer to free
    > *
    > * Drop a reference to the buffer and free it if the usage count has
    > * hit zero.
    > */
    > static inline void kfree_skb(struct sk_buff *skb)
    > {
    > if (likely(atomic_read(&skb->users) == 1))
    > smp_rmb();
    > else if (likely(!atomic_dec_and_test(&skb->users)))
    > return;
    > __kfree_skb(skb);
    > }
    >
    >
    > This is a valid optimization : an atomic_dec_and_test() is very expensive.

    It is a valid optimization if you will normally have only one user
    like a skb. For other structures that frequently have many users I'm
    not at all certain it is a useful optimization.

    Eric
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-01-30 22:54    [W:0.040 / U:62.856 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site