Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
> -Original Message-
> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Ananyev, Konstantin
> Sent: Wednesday, February 14, 2018 12:35 PM
> To: Richardson, Bruce
> Cc: Yongseok Koh ; Olivier Matz ;
> dev@dpdk.org
> Subject: Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
>
>
>
> > -Original Message-
> > From: Richardson, Bruce
> > Sent: Wednesday, February 14, 2018 12:12 PM
> > To: Ananyev, Konstantin
> > Cc: Yongseok Koh ; Olivier Matz
> > ; dev@dpdk.org
> > Subject: Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
> >
> > On Wed, Feb 14, 2018 at 12:03:55PM +, Ananyev, Konstantin wrote:
> > >
> > >
> > > > -Original Message-
> > > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Ananyev, Konstantin
> > > > Sent: Wednesday, February 14, 2018 11:48 AM
> > > > To: Yongseok Koh ; Olivier Matz
> > > >
> > > > Cc: dev@dpdk.org
> > > > Subject: Re: [dpdk-dev] Accessing 2nd cacheline in
> > > > rte_pktmbuf_prefree_seg()
> > > >
> > > > Hi Yongseok,
> > > >
> > > > > > On Feb 13, 2018, at 2:45 PM, Yongseok Koh
> > > > > > wrote:
> > > > > >
> > > > > > Hi Olivier
> > > > > >
> > > > > > I'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead
> > > > > > of
> > > > > > m->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs
> > > > > > seems beneficial
> > > > > > to the cases where almost mbufs have single segment.
> > > > > >
> > > > > > A customer reported high rate of cache misses in the code and I
> > > > > > thought the
> > > > > > following patch could be helpful. I haven't had them try it yet but
> > > > > > just wanted
> > > > > > to hear from you.
> > > > > >
> > > > > > I'd appreciate if you can review this idea.
> > > > > >
> > > > > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > > > > > index 62740254d..96edbcb9e 100644
> > > > > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > > > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > > > > @@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > > > > >if (RTE_MBUF_INDIRECT(m))
> > > > > >rte_pktmbuf_detach(m);
> > > > > >
> > > > > > - if (m->next != NULL) {
> > > > > > + if (m->nb_segs > 1) {
> > > > > >m->next = NULL;
> > > > > >m->nb_segs = 1;
> > > > > >}
> > > > > > @@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > > > > >if (RTE_MBUF_INDIRECT(m))
> > > > > >rte_pktmbuf_detach(m);
> > > > > >
> > > > > > - if (m->next != NULL) {
> > > > > > + if (m->nb_segs > 1) {
> > > > > >m->next = NULL;
> > > > > >m->nb_segs = 1;
> > > > > >}
> > > > >
> > > > > Well, m->pool in the 2nd cacheline has to be accessed anyway in order
> > > > > to put it back to the mempool.
> > > > > It looks like the cache miss is unavoidable.
> > > >
> > > > As a thought: in theory PMD can store pool pointer together with each
> > > > mbuf it has to free,
> > > > then it could be something like:
> > > >
> > > > if (rte_pktmbuf_prefree_seg(m[x] != NULL)
> > > >rte_mempool_put(pool[x], m[x]);
> > > >
> > > > Then what you suggested above might help.
> > >
> > > After another thought - we have to check m->next not m->nb_segs.
> > > There could be a situations where nb_segs==1, but m->next != NULL
> > > (2-nd segment of the 3 segment packet for example).
> > > So probably we have to keep it as it is.
> > > Sorry for the noise
> > > Konstantin
> >
> > It's still worth considering as an option.
Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
> -Original Message-
> From: Richardson, Bruce
> Sent: Wednesday, February 14, 2018 12:12 PM
> To: Ananyev, Konstantin
> Cc: Yongseok Koh ; Olivier Matz ;
> dev@dpdk.org
> Subject: Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
>
> On Wed, Feb 14, 2018 at 12:03:55PM +, Ananyev, Konstantin wrote:
> >
> >
> > > -Original Message-
> > > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Ananyev, Konstantin
> > > Sent: Wednesday, February 14, 2018 11:48 AM
> > > To: Yongseok Koh ; Olivier Matz
> > >
> > > Cc: dev@dpdk.org
> > > Subject: Re: [dpdk-dev] Accessing 2nd cacheline in
> > > rte_pktmbuf_prefree_seg()
> > >
> > > Hi Yongseok,
> > >
> > > > > On Feb 13, 2018, at 2:45 PM, Yongseok Koh wrote:
> > > > >
> > > > > Hi Olivier
> > > > >
> > > > > I'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead of
> > > > > m->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs seems
> > > > > beneficial
> > > > > to the cases where almost mbufs have single segment.
> > > > >
> > > > > A customer reported high rate of cache misses in the code and I
> > > > > thought the
> > > > > following patch could be helpful. I haven't had them try it yet but
> > > > > just wanted
> > > > > to hear from you.
> > > > >
> > > > > I'd appreciate if you can review this idea.
> > > > >
> > > > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > > > > index 62740254d..96edbcb9e 100644
> > > > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > > > @@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > > > >if (RTE_MBUF_INDIRECT(m))
> > > > >rte_pktmbuf_detach(m);
> > > > >
> > > > > - if (m->next != NULL) {
> > > > > + if (m->nb_segs > 1) {
> > > > >m->next = NULL;
> > > > >m->nb_segs = 1;
> > > > >}
> > > > > @@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > > > >if (RTE_MBUF_INDIRECT(m))
> > > > >rte_pktmbuf_detach(m);
> > > > >
> > > > > - if (m->next != NULL) {
> > > > > + if (m->nb_segs > 1) {
> > > > >m->next = NULL;
> > > > >m->nb_segs = 1;
> > > > >}
> > > >
> > > > Well, m->pool in the 2nd cacheline has to be accessed anyway in order
> > > > to put it back to the mempool.
> > > > It looks like the cache miss is unavoidable.
> > >
> > > As a thought: in theory PMD can store pool pointer together with each
> > > mbuf it has to free,
> > > then it could be something like:
> > >
> > > if (rte_pktmbuf_prefree_seg(m[x] != NULL)
> > >rte_mempool_put(pool[x], m[x]);
> > >
> > > Then what you suggested above might help.
> >
> > After another thought - we have to check m->next not m->nb_segs.
> > There could be a situations where nb_segs==1, but m->next != NULL
> > (2-nd segment of the 3 segment packet for example).
> > So probably we have to keep it as it is.
> > Sorry for the noise
> > Konstantin
>
> It's still worth considering as an option. We could check nb_segs for
> the first segment of a packet and thereafter iterate using the next
> pointer.
In multi-seg case PMD frees segments (not packets).
It could happen that first segment would be already freed while the second
still not.
> It means that your idea of storing the pool pointer for each
> mbuf becomes useful for single-segment packets.
But then we'll have to support 2 different flavors of prefree_seg().
Alternative would be to change all PMDs multi-seg TX so when first segment is
going to be freed we update nb_segs for the second and so on.
Both options seems like too much hassle.
Konstantin
Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
On Wed, Feb 14, 2018 at 12:03:55PM +, Ananyev, Konstantin wrote:
>
>
> > -Original Message-
> > From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Ananyev, Konstantin
> > Sent: Wednesday, February 14, 2018 11:48 AM
> > To: Yongseok Koh ; Olivier Matz
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
> >
> > Hi Yongseok,
> >
> > > > On Feb 13, 2018, at 2:45 PM, Yongseok Koh wrote:
> > > >
> > > > Hi Olivier
> > > >
> > > > I'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead of
> > > > m->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs seems
> > > > beneficial
> > > > to the cases where almost mbufs have single segment.
> > > >
> > > > A customer reported high rate of cache misses in the code and I thought
> > > > the
> > > > following patch could be helpful. I haven't had them try it yet but
> > > > just wanted
> > > > to hear from you.
> > > >
> > > > I'd appreciate if you can review this idea.
> > > >
> > > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > > > index 62740254d..96edbcb9e 100644
> > > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > > @@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > > >if (RTE_MBUF_INDIRECT(m))
> > > >rte_pktmbuf_detach(m);
> > > >
> > > > - if (m->next != NULL) {
> > > > + if (m->nb_segs > 1) {
> > > >m->next = NULL;
> > > >m->nb_segs = 1;
> > > >}
> > > > @@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > > >if (RTE_MBUF_INDIRECT(m))
> > > >rte_pktmbuf_detach(m);
> > > >
> > > > - if (m->next != NULL) {
> > > > + if (m->nb_segs > 1) {
> > > >m->next = NULL;
> > > >m->nb_segs = 1;
> > > >}
> > >
> > > Well, m->pool in the 2nd cacheline has to be accessed anyway in order to
> > > put it back to the mempool.
> > > It looks like the cache miss is unavoidable.
> >
> > As a thought: in theory PMD can store pool pointer together with each mbuf
> > it has to free,
> > then it could be something like:
> >
> > if (rte_pktmbuf_prefree_seg(m[x] != NULL)
> >rte_mempool_put(pool[x], m[x]);
> >
> > Then what you suggested above might help.
>
> After another thought - we have to check m->next not m->nb_segs.
> There could be a situations where nb_segs==1, but m->next != NULL
> (2-nd segment of the 3 segment packet for example).
> So probably we have to keep it as it is.
> Sorry for the noise
> Konstantin
It's still worth considering as an option. We could check nb_segs for
the first segment of a packet and thereafter iterate using the next
pointer. It means that your idea of storing the pool pointer for each
mbuf becomes useful for single-segment packets.
/Bruce
Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
> -Original Message-
> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Ananyev, Konstantin
> Sent: Wednesday, February 14, 2018 11:48 AM
> To: Yongseok Koh ; Olivier Matz
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
>
> Hi Yongseok,
>
> > > On Feb 13, 2018, at 2:45 PM, Yongseok Koh wrote:
> > >
> > > Hi Olivier
> > >
> > > I'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead of
> > > m->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs seems
> > > beneficial
> > > to the cases where almost mbufs have single segment.
> > >
> > > A customer reported high rate of cache misses in the code and I thought
> > > the
> > > following patch could be helpful. I haven't had them try it yet but just
> > > wanted
> > > to hear from you.
> > >
> > > I'd appreciate if you can review this idea.
> > >
> > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > > index 62740254d..96edbcb9e 100644
> > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > @@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > >if (RTE_MBUF_INDIRECT(m))
> > >rte_pktmbuf_detach(m);
> > >
> > > - if (m->next != NULL) {
> > > + if (m->nb_segs > 1) {
> > >m->next = NULL;
> > >m->nb_segs = 1;
> > >}
> > > @@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> > >if (RTE_MBUF_INDIRECT(m))
> > >rte_pktmbuf_detach(m);
> > >
> > > - if (m->next != NULL) {
> > > + if (m->nb_segs > 1) {
> > >m->next = NULL;
> > >m->nb_segs = 1;
> > >}
> >
> > Well, m->pool in the 2nd cacheline has to be accessed anyway in order to
> > put it back to the mempool.
> > It looks like the cache miss is unavoidable.
>
> As a thought: in theory PMD can store pool pointer together with each mbuf it
> has to free,
> then it could be something like:
>
> if (rte_pktmbuf_prefree_seg(m[x] != NULL)
>rte_mempool_put(pool[x], m[x]);
>
> Then what you suggested above might help.
After another thought - we have to check m->next not m->nb_segs.
There could be a situations where nb_segs==1, but m->next != NULL
(2-nd segment of the 3 segment packet for example).
So probably we have to keep it as it is.
Sorry for the noise
Konstantin
Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
Hi Yongseok,
> > On Feb 13, 2018, at 2:45 PM, Yongseok Koh wrote:
> >
> > Hi Olivier
> >
> > I'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead of
> > m->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs seems
> > beneficial
> > to the cases where almost mbufs have single segment.
> >
> > A customer reported high rate of cache misses in the code and I thought the
> > following patch could be helpful. I haven't had them try it yet but just
> > wanted
> > to hear from you.
> >
> > I'd appreciate if you can review this idea.
> >
> > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > index 62740254d..96edbcb9e 100644
> > --- a/lib/librte_mbuf/rte_mbuf.h
> > +++ b/lib/librte_mbuf/rte_mbuf.h
> > @@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> >if (RTE_MBUF_INDIRECT(m))
> >rte_pktmbuf_detach(m);
> >
> > - if (m->next != NULL) {
> > + if (m->nb_segs > 1) {
> >m->next = NULL;
> >m->nb_segs = 1;
> >}
> > @@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
> >if (RTE_MBUF_INDIRECT(m))
> >rte_pktmbuf_detach(m);
> >
> > - if (m->next != NULL) {
> > + if (m->nb_segs > 1) {
> >m->next = NULL;
> >m->nb_segs = 1;
> >}
>
> Well, m->pool in the 2nd cacheline has to be accessed anyway in order to put
> it back to the mempool.
> It looks like the cache miss is unavoidable.
As a thought: in theory PMD can store pool pointer together with each mbuf it
has to free,
then it could be something like:
if (rte_pktmbuf_prefree_seg(m[x] != NULL)
rte_mempool_put(pool[x], m[x]);
Then what you suggested above might help.
Konstantin
Re: [dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
> On Feb 13, 2018, at 2:45 PM, Yongseok Koh wrote:
>
> Hi Olivier
>
> I'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead of
> m->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs seems
> beneficial
> to the cases where almost mbufs have single segment.
>
> A customer reported high rate of cache misses in the code and I thought the
> following patch could be helpful. I haven't had them try it yet but just
> wanted
> to hear from you.
>
> I'd appreciate if you can review this idea.
>
> diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> index 62740254d..96edbcb9e 100644
> --- a/lib/librte_mbuf/rte_mbuf.h
> +++ b/lib/librte_mbuf/rte_mbuf.h
> @@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>if (RTE_MBUF_INDIRECT(m))
>rte_pktmbuf_detach(m);
>
> - if (m->next != NULL) {
> + if (m->nb_segs > 1) {
>m->next = NULL;
>m->nb_segs = 1;
>}
> @@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
>if (RTE_MBUF_INDIRECT(m))
>rte_pktmbuf_detach(m);
>
> - if (m->next != NULL) {
> + if (m->nb_segs > 1) {
>m->next = NULL;
>m->nb_segs = 1;
>}
Well, m->pool in the 2nd cacheline has to be accessed anyway in order to put it
back to the mempool.
It looks like the cache miss is unavoidable.
Thanks
Yongseok
[dpdk-dev] Accessing 2nd cacheline in rte_pktmbuf_prefree_seg()
Hi Olivier
I'm wondering why rte_pktmbuf_prefree_seg() checks m->next instead of
m->nb_segs? As 'next' is in the 2nd cacheline, checking nb_segs seems beneficial
to the cases where almost mbufs have single segment.
A customer reported high rate of cache misses in the code and I thought the
following patch could be helpful. I haven't had them try it yet but just wanted
to hear from you.
I'd appreciate if you can review this idea.
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 62740254d..96edbcb9e 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -1398,7 +1398,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
if (RTE_MBUF_INDIRECT(m))
rte_pktmbuf_detach(m);
- if (m->next != NULL) {
+ if (m->nb_segs > 1) {
m->next = NULL;
m->nb_segs = 1;
}
@@ -1410,7 +1410,7 @@ rte_pktmbuf_prefree_seg(struct rte_mbuf *m)
if (RTE_MBUF_INDIRECT(m))
rte_pktmbuf_detach(m);
- if (m->next != NULL) {
+ if (m->nb_segs > 1) {
m->next = NULL;
m->nb_segs = 1;
}
Thanks,
Yongseok
