[ovs-dev] [PATCH v9 5/5] dpif-netdev: add specialized generic scalar functions
Malvika Gupta
Malvika.Gupta at arm.com
Wed Jun 19 18:34:10 UTC 2019
Hi Harry
Thanks for your reply. I have some last few things I wanted to clarify. Please see my inline comments below.
> -----Original Message-----
> From: Van Haaren, Harry <harry.van.haaren at intel.com>
> Sent: Wednesday, June 19, 2019 11:22 AM
> To: Malvika Gupta <Malvika.Gupta at arm.com>
> Cc: Yanqin Wei (Arm Technology China) <Yanqin.Wei at arm.com>; nd
> <nd at arm.com>; dev at openvswitch.org
> Subject: RE: [ovs-dev] [PATCH v9 5/5] dpif-netdev: add specialized generic
> scalar functions
>
> > -----Original Message-----
> > From: Malvika Gupta [mailto:Malvika.Gupta at arm.com]
> > Sent: Wednesday, June 19, 2019 5:17 PM
> > To: Van Haaren, Harry <harry.van.haaren at intel.com>
> > Cc: Yanqin Wei (Arm Technology China) <Yanqin.Wei at arm.com>; nd
> > <nd at arm.com>; dev at openvswitch.org
> > Subject: RE: [ovs-dev] [PATCH v9 5/5] dpif-netdev: add specialized
> > generic scalar functions
> >
> > Hi Harry,
>
> Hi Malvika,
>
>
> > I would like to test your patch on ARM platforms and report any
> > performance improvement. Can you please tell me the test vectors you
> > used to match the subtables that call the specialized lookup
> > functions, i.e., dpcls_subtable_lookup_mf_u0w5_u1w1,
> > dpcls_subtable_lookup_mf_u0w4_u1w1, and
> > dpcls_subtable_lookup_mf_u0w4_u1w0? And how did you make that
> > distinction with traffic patterns, i.e., which traffic pattern would match with
> which subtable lookup?
>
> I was just running Eth/IPv4/UDP data, and using OvS to do Phy to Phy
> forwarding.
>
> ./utilities/ovs-ofctl add-flow br0 in_port=1,action=output:2 ./utilities/ovs-
> ofctl add-flow br0 in_port=2,action=output:1
>
> This is an extremely simple setup, however it is enough to showcase value of
> the patches here.
>
> By changing traffic to Eth/IPv4 and Eth alone, you can change the # of
> miniflow items, and hit the different u0_w5_u1_w0 cases :)
>
1. Are you also sending combinations of traffic flows at the same time? Like UDP/IPv4/Eth is one traffic flow, raw IP could be another and Eth packets only is a third flow. Did you also test by say, sending these 3 flows together which would all hit different subtables or just one kind of traffic flow at a time?
2. Just to clarify, packet size is 64B, right?
I am sorry if these seem trivial but I just wanted to have a clear understanding of the testing environment.
Thanks!
> If you have suggestions for other subtables to special case, please post the
> u0_wX_u1_wY values that you'd like to see, and I'll add them to the patchset.
>
>
> > Thank you,
> > Malvika Gupta
>
> Testing welcomed, thanks! -Harry
>
> > > -----Original Message-----
> > > From: ovs-dev-bounces at openvswitch.org <ovs-dev-
> > > bounces at openvswitch.org> On Behalf Of Harry van Haaren
> > > Sent: Wednesday, May 8, 2019 11:13 PM
> > > To: ovs-dev at openvswitch.org
> > > Cc: i.maximets at samsung.com
> > > Subject: [ovs-dev] [PATCH v9 5/5] dpif-netdev: add specialized
> > > generic
> > scalar
> > > functions
> > >
> > > This commit adds a number of specialized functions, that handle
> > > common miniflow fingerprints. This enables compiler optimization,
> > > resulting in
> > higher
> > > performance. Below a quick description of how this optimization
> > > actually works;
> > >
> > > "Specialized functions" are "instances" of the generic
> > > implementation, but the compiler is given extra context when
> > > compiling. In the case of
> > iterating
> > > miniflow datastructures, the most interesting value to enable
> > > compile time optimizations is the loop trip count per unit.
> > >
> > > In order to create a specialized function, there is a generic
> > implementation,
> > > which uses a for() loop without the compiler knowing the loop trip
> > > count
> > at
> > > compile time. The loop trip count is passed in as an argument to the
> > function:
> > >
> > > uint32_t miniflow_impl_generic(struct miniflow *mf, uint32_t loop_count)
> {
> > > for(uint32_t i = 0; i < loop_count; i++)
> > > // do work
> > > }
> > >
> > > In order to "specialize" the function, we call the generic
> > > implementation
> > with
> > > hard-coded numbers - these are compile time constants!
> > >
> > > uint32_t miniflow_impl_loop5(struct miniflow *mf, uint32_t loop_count)
> {
> > > // use hard coded constant for compile-time constant-propogation
> > > return miniflow_impl_generic(mf, 5); }
> > >
> > > Given the compiler is aware of the loop trip count at compile time,
> > > it can perform an optimization known as "constant propogation".
> > > Combined with inlining of the miniflow_impl_generic() function, the
> > > compiler is now
> > enabled
> > > to *compile time* unroll the loop 5x, and produce "flat" code.
> > >
> > > The last step to using the specialized functions is to utilize a
> > > function-
> > pointer
> > > to choose the specialized (or generic) implementation.
> > > The selection of the function pointer is performed at subtable
> > > creation
> > time,
> > > when miniflow fingerprint of the subtable is known. This technique
> > > is
> > known
> > > as "multiple dispatch" in some literature, as it uses multiple items
> > > of information (miniflow bit counts) to select the dispatch function.
> > >
> > > By pointing the function pointer at the optimized implementation,
> > > OvS benefits from the compile time optimizations at runtime.
> > >
> > > Signed-off-by: Harry van Haaren <harry.van.haaren at intel.com>
> > >
> > > ---
> > >
> > > v8:
> > > - Rework to use blocks_cache from the dpcls instance, to avoid variable
> > > lenght arrays in the data-path.
> > > ---
> > > lib/dpif-netdev-lookup-generic.c | 83 +++++++++++++++++++++++++++++-
> --
> > > lib/dpif-netdev.c | 9 +++-
> > > lib/dpif-netdev.h | 8 +++
> > > 3 files changed, 90 insertions(+), 10 deletions(-)
> > >
> > > diff --git a/lib/dpif-netdev-lookup-generic.c
> > > b/lib/dpif-netdev-lookup- generic.c index 901d28ff0..ba2d024cc
> > > 100644
> > > --- a/lib/dpif-netdev-lookup-generic.c
> > > +++ b/lib/dpif-netdev-lookup-generic.c
> > > @@ -100,11 +100,11 @@ netdev_flow_key_flatten(const struct
> > > netdev_flow_key * restrict key,
> > >
> > > /* Unit 0 flattening */
> > > netdev_flow_key_flatten_unit(&pkt_blocks[0],
> > > - &tbl_blocks[0],
> > > - &mf_masks[0],
> > > - &blocks_scratch[0],
> > > - pkt_bits_u0,
> > > - u0_count);
> > > + &tbl_blocks[0],
> > > + &mf_masks[0],
> > > + &blocks_scratch[0],
> > > + pkt_bits_u0,
> > > + u0_count);
> > >
> > > /* Unit 1 flattening:
> > > * Move the pointers forward in the arrays based on u0 offsets, NOTE:
> > > @@ -225,7 +225,74 @@ dpcls_subtable_lookup_generic(struct
> > > dpcls_subtable *subtable,
> > > const struct netdev_flow_key *keys[],
> > > struct dpcls_rule **rules) {
> > > - return lookup_generic_impl(subtable, blocks_scratch, keys_map,
> > keys,
> > > - rules, subtable->mf_bits_set_unit0,
> > > - subtable->mf_bits_set_unit1);
> > > + /* Here the runtime subtable->mf_bits counts are used, which
> > > + forces
> > the
> > > + * compiler to iterate normal for() loops. Due to this
> > > + limitation in
> > the
> > > + * compilers available optimizations, this function has lower
> > performance
> > > + * than the below specialized functions.
> > > + */
> > > + return lookup_generic_impl(subtable, blocks_scratch, keys_map,
> > > + keys,
> > > rules,
> > > + subtable->mf_bits_set_unit0,
> > > + subtable->mf_bits_set_unit1); }
> > > +
> > > +static uint32_t
> > > +dpcls_subtable_lookup_mf_u0w5_u1w1(struct dpcls_subtable
> *subtable,
> > > + uint64_t *blocks_scratch,
> > > + uint32_t keys_map,
> > > + const struct netdev_flow_key *keys[],
> > > + struct dpcls_rule **rules) {
> > > + /* hard coded bit counts - enables compile time loop unrolling, and
> > > + * generating of optimized code-sequences due to loop unrolled code.
> > > + */
> > > + return lookup_generic_impl(subtable, blocks_scratch, keys_map,
> > > +keys,
> > > rules,
> > > + 5, 1); }
> > > +
> > > +static uint32_t
> > > +dpcls_subtable_lookup_mf_u0w4_u1w1(struct dpcls_subtable
> *subtable,
> > > + uint64_t *blocks_scratch,
> > > + uint32_t keys_map,
> > > + const struct netdev_flow_key *keys[],
> > > + struct dpcls_rule **rules) {
> > > + return lookup_generic_impl(subtable, blocks_scratch, keys_map,
> > > +keys,
> > > rules,
> > > + 4, 1); }
> > > +
> > > +static uint32_t
> > > +dpcls_subtable_lookup_mf_u0w4_u1w0(struct dpcls_subtable
> *subtable,
> > > + uint64_t *blocks_scratch,
> > > + uint32_t keys_map,
> > > + const struct netdev_flow_key *keys[],
> > > + struct dpcls_rule **rules) {
> > > + return lookup_generic_impl(subtable, blocks_scratch, keys_map,
> > > +keys,
> > > rules,
> > > + 4, 0); }
> > > +
> > > +/* Probe function to lookup an available specialized function.
> > > + * If capable to run the requested miniflow fingerprint, this
> > > +function returns
> > > + * the most optimal implementation for that miniflow fingerprint.
> > > + * @retval FunctionAddress A valid function to handle the miniflow
> > > +bit pattern
> > > + * @retval 0 The requested miniflow is not supported here, NULL is
> > > +returned */ dpcls_subtable_lookup_func
> > > +dpcls_subtable_generic_probe(uint32_t u0_bits, uint32_t u1_bits) {
> > > + dpcls_subtable_lookup_func f = NULL;
> > > +
> > > + if (u0_bits == 5 && u1_bits == 1) {
> > > + f = dpcls_subtable_lookup_mf_u0w5_u1w1;
> > > + } else if (u0_bits == 4 && u1_bits == 1) {
> > > + f = dpcls_subtable_lookup_mf_u0w4_u1w1;
> > > + } else if (u0_bits == 4 && u1_bits == 0) {
> > > + f = dpcls_subtable_lookup_mf_u0w4_u1w0;
> > > + }
> > > +
> > > + if (f) {
> > > + VLOG_INFO("Subtable using Generic Optimized for u0 %d, u1 %d\n",
> > > + u0_bits, u1_bits);
> > > + }
> > > + return f;
> > > }
> > > diff --git a/lib/dpif-netdev.c b/lib/dpif-netdev.c index
> > 33b93cfdf..23fc5b7a6
> > > 100644
> > > --- a/lib/dpif-netdev.c
> > > +++ b/lib/dpif-netdev.c
> > > @@ -7623,8 +7623,13 @@ dpcls_create_subtable(struct dpcls *cls,
> > > const struct netdev_flow_key *mask)
> > > cls->blocks_scratch_size = blocks_required_per_pkt;
> > > }
> > >
> > > - /* Assign the generic lookup - this works with any miniflow
> > fingerprint */
> > > - subtable->lookup_func = dpcls_subtable_lookup_generic;
> > > + /* Probe for an optimmized variant */
> > > + subtable->lookup_func = dpcls_subtable_generic_probe(unit0,
> > > + unit1);
> > > +
> > > + /* If not set, assign generic lookup - this works with any
> > > + miniflow
> > */
> > > + if (!subtable->lookup_func) {
> > > + subtable->lookup_func = dpcls_subtable_lookup_generic;
> > > + }
> > >
> > > cmap_insert(&cls->subtables_map, &subtable->cmap_node, mask-
> >hash);
> > > /* Add the new subtable at the end of the pvector (with no hits
> > > yet)
> > */ diff
> > > --git a/lib/dpif-netdev.h b/lib/dpif-netdev.h index
> > > 9263256a9..123eabad7
> > > 100644
> > > --- a/lib/dpif-netdev.h
> > > +++ b/lib/dpif-netdev.h
> > > @@ -70,6 +70,14 @@ typedef uint32_t
> > > (*dpcls_subtable_lookup_func)(struct dpcls_subtable *subtable,
> > > const struct netdev_flow_key *keys[],
> > > struct dpcls_rule **rules);
> > >
> > > +/* Probe function to select a specialized version of the generic
> > > +lookup
> > > + * implementation. This provides performance benefit due to
> > > +compile-time
> > > + * optimizations such as loop-unrolling. These are enabled by the
> > > +compile-time
> > > + * constants in the specific function implementations.
> > > + */
> > > +dpcls_subtable_lookup_func
> > > +dpcls_subtable_generic_probe(uint32_t u0_bit_count, uint32_t
> > > +u1_bit_count);
> > > +
> > > /* Prototype for generic lookup func, using same code path as
> > > before */ uint32_t dpcls_subtable_lookup_generic(struct
> > > dpcls_subtable *subtable,
> > > --
> > > 2.17.1
> > >
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