lkml.org 
[lkml]   [2011]   [May]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [PATCH V5 2/6 net-next] netdevice.h: Add zero-copy flag in netdevice
    W dniu 18 maja 2011 01:44 użytkownik Shirley Ma <mashirle@us.ibm.com> napisał:
    > On Wed, 2011-05-18 at 00:58 +0200, Michał Mirosław wrote:
    >> W dniu 18 maja 2011 00:28 użytkownik Shirley Ma <mashirle@us.ibm.com>
    >> napisał:
    >> > On Tue, 2011-05-17 at 23:48 +0200, Michał Mirosław wrote:
    >> >> 2011/5/17 Shirley Ma <mashirle@us.ibm.com>:
    >> >> > Looks like to use a new flag requires more time/work. I am
    >> thinking
    >> >> > whether we can just use HIGHDMA flag to enable zero-copy in
    >> macvtap
    >> >> to
    >> >> > avoid the new flag for now since mavctap uses real NICs as lower
    >> >> device?
    >> >>
    >> >> Is there any other restriction besides requiring driver to not
    >> recycle
    >> >> the skb? Are there any drivers that recycle TX skbs?
    >> > Not more other restrictions, skb clone is OK. pskb_expand_head()
    >> looks
    >> > OK to me from code review.
    >>
    >> > Currently there is no drivers recycle TX skbs.
    >>
    >> So why do you require the target device to have some flags at all?
    > We could use macvtap to check lower device HIGHDMA to enable zero-copy,
    > but I am not sure whether it is sufficient. If it's sufficient then we
    > don't need to use a new flag here. To be safe, it's better to use a new
    > flag to enable each device who can pass zero-copy test.

    >> Do I understand correctly, that this zero-copy feature is about
    >> packets received from VMs?
    > Yes, packets sent from VMs, and received in local host for TX zero-copy
    > here.

    What is the zero-copy test? On some arches the HIGHDMA is not needed
    at all so might be not enabled on anything. It looks like the correct
    test would be per-packet check of !illegal_highdma() or maybe
    NETIF_F_SG as returned from harmonize_features(). For virtual devices
    or other software forwarding this might lead to skb_linearize() in
    some cases, but is it that bad?

    Best Regards,
    Michał Mirosław
    --
    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: 2011-05-18 11:09    [W:8.898 / U:0.004 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site