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Date: Wed, 21 Aug 2019 15:46:23 +0200
From: "Eelco Chaudron" <echaudro@...hat.com>
To: "Magnus Karlsson" <magnus.karlsson@...il.com>
Cc: "Network Development" <netdev@...r.kernel.org>,
"Alexei Starovoitov" <ast@...nel.org>,
"Daniel Borkmann" <daniel@...earbox.net>,
"Martin KaFai Lau" <kafai@...com>,
"Song Liu" <songliubraving@...com>, "Yonghong Song" <yhs@...com>,
"Andrii Nakryiko" <andrii.nakryiko@...il.com>
Subject: Re: [PATCH bpf-next v4] libbpf: add xsk_ring_prod__nb_free() function
On 21 Aug 2019, at 15:11, Magnus Karlsson wrote:
> On Wed, Aug 14, 2019 at 3:51 PM Eelco Chaudron <echaudro@...hat.com>
> wrote:
>>
>> When an AF_XDP application received X packets, it does not mean X
>> frames can be stuffed into the producer ring. To make it easier for
>> AF_XDP applications this API allows them to check how many frames can
>> be added into the ring.
>>
>> The patch below looks like a name change only, but the xsk_prod__
>> prefix denotes that this API is exposed to be used by applications.
>>
>> Besides, if you set the nb value to the size of the ring, you will
>> get the exact amount of slots available, at the cost of performance
>> (you touch shared state for sure). nb is there to limit the
>> touching of the shared state.
>>
>> Also the example xdpsock application has been modified to use this
>> new API, so it's also able to process flows at a 1pps rate on veth
>> interfaces.
>
> My apologies for the late reply and thank you for working on this. So
> what kind of performance difference do you see with your modified
> xdpsock application on a regular NIC for txpush and l2fwd? If there is
> basically no difference or it is faster, we can go ahead and accept
> this. But if the difference is large, we might consider to have two
> versions of txpush and l2fwd as the regular NICs do not need this. Or
> we optimize your code so that it becomes as fast as the previous
> version.
For both operation modes, I ran 5 test with and without the changes
applied using an iexgb connecting to a XENA tester. The throughput
numbers were within the standard deviation, so no noticeable performance
gain or drop.
Let me know if this is enough, if not I can rebuild the setup and do
some more tests.
> /Magnus
>
>> Signed-off-by: Eelco Chaudron <echaudro@...hat.com>
>> ---
>>
>> v3 -> v4
>> - Cleanedup commit message
>> - Updated AF_XDP sample application to use this new API
>>
>> v2 -> v3
>> - Removed cache by pass option
>>
>> v1 -> v2
>> - Renamed xsk_ring_prod__free() to xsk_ring_prod__nb_free()
>> - Add caching so it will only touch global state when needed
>>
>> samples/bpf/xdpsock_user.c | 109
>> ++++++++++++++++++++++++++++---------
>> tools/lib/bpf/xsk.h | 4 +-
>> 2 files changed, 86 insertions(+), 27 deletions(-)
>>
>> diff --git a/samples/bpf/xdpsock_user.c b/samples/bpf/xdpsock_user.c
>> index 93eaaf7239b2..87115e233b54 100644
>> --- a/samples/bpf/xdpsock_user.c
>> +++ b/samples/bpf/xdpsock_user.c
>> @@ -461,9 +461,13 @@ static void kick_tx(struct xsk_socket_info *xsk)
>>
>> static inline void complete_tx_l2fwd(struct xsk_socket_info *xsk)
>> {
>> - u32 idx_cq = 0, idx_fq = 0;
>> - unsigned int rcvd;
>> + static u64 free_frames[NUM_FRAMES];
>> + static size_t nr_free_frames;
>> +
>> + u32 idx_cq = 0, idx_fq = 0, free_slots;
>> + unsigned int rcvd, i;
>> size_t ndescs;
>> + int ret;
>>
>> if (!xsk->outstanding_tx)
>> return;
>> @@ -474,27 +478,52 @@ static inline void complete_tx_l2fwd(struct
>> xsk_socket_info *xsk)
>>
>> /* re-add completed Tx buffers */
>> rcvd = xsk_ring_cons__peek(&xsk->umem->cq, ndescs, &idx_cq);
>> - if (rcvd > 0) {
>> - unsigned int i;
>> - int ret;
>> + if (!rcvd)
>> + return;
>>
>> - ret = xsk_ring_prod__reserve(&xsk->umem->fq, rcvd,
>> &idx_fq);
>> - while (ret != rcvd) {
>> - if (ret < 0)
>> - exit_with_error(-ret);
>> - ret = xsk_ring_prod__reserve(&xsk->umem->fq,
>> rcvd,
>> - &idx_fq);
>> - }
>> - for (i = 0; i < rcvd; i++)
>> + /* When xsk_ring_cons__peek() for example returns that 5
>> packets
>> + * have been received, it does not automatically mean that
>> + * xsk_ring_prod__reserve() will have 5 slots available. You
>> will
>> + * see this, for example, when using a veth interface due to
>> the
>> + * RX_BATCH_SIZE used by the generic driver.
>> + *
>> + * In this example we store unused buffers and try to
>> re-stock
>> + * them the next iteration.
>> + */
>> +
>> + free_slots = xsk_prod__nb_free(&xsk->umem->fq, rcvd +
>> nr_free_frames);
>> + if (free_slots > rcvd + nr_free_frames)
>> + free_slots = rcvd + nr_free_frames;
>> +
>> + ret = xsk_ring_prod__reserve(&xsk->umem->fq, free_slots,
>> &idx_fq);
>> + while (ret != free_slots) {
>> + if (ret < 0)
>> + exit_with_error(-ret);
>> + ret = xsk_ring_prod__reserve(&xsk->umem->fq,
>> free_slots,
>> + &idx_fq);
>> + }
>> + for (i = 0; i < rcvd; i++) {
>> + u64 addr = *xsk_ring_cons__comp_addr(&xsk->umem->cq,
>> idx_cq++);
>> +
>> + if (i < free_slots)
>> *xsk_ring_prod__fill_addr(&xsk->umem->fq,
>> idx_fq++) =
>> -
>> *xsk_ring_cons__comp_addr(&xsk->umem->cq,
>> - idx_cq++);
>> + addr;
>> + else
>> + free_frames[nr_free_frames++] = addr;
>> + }
>>
>> - xsk_ring_prod__submit(&xsk->umem->fq, rcvd);
>> - xsk_ring_cons__release(&xsk->umem->cq, rcvd);
>> - xsk->outstanding_tx -= rcvd;
>> - xsk->tx_npkts += rcvd;
>> + if (free_slots > rcvd) {
>> + for (i = 0; i < (free_slots - rcvd); i++) {
>> + u64 addr = free_frames[--nr_free_frames];
>> + *xsk_ring_prod__fill_addr(&xsk->umem->fq,
>> idx_fq++) =
>> + addr;
>> + }
>> }
>> +
>> + xsk_ring_prod__submit(&xsk->umem->fq, free_slots);
>> + xsk_ring_cons__release(&xsk->umem->cq, rcvd);
>> + xsk->outstanding_tx -= rcvd;
>> + xsk->tx_npkts += rcvd;
>> }
>>
>> static inline void complete_tx_only(struct xsk_socket_info *xsk)
>> @@ -517,19 +546,37 @@ static inline void complete_tx_only(struct
>> xsk_socket_info *xsk)
>>
>> static void rx_drop(struct xsk_socket_info *xsk)
>> {
>> + static u64 free_frames[NUM_FRAMES];
>> + static size_t nr_free_frames;
>> +
>> unsigned int rcvd, i;
>> - u32 idx_rx = 0, idx_fq = 0;
>> + u32 idx_rx = 0, idx_fq = 0, free_slots;
>> int ret;
>>
>> rcvd = xsk_ring_cons__peek(&xsk->rx, BATCH_SIZE, &idx_rx);
>> if (!rcvd)
>> return;
>>
>> - ret = xsk_ring_prod__reserve(&xsk->umem->fq, rcvd, &idx_fq);
>> - while (ret != rcvd) {
>> + /* When xsk_ring_cons__peek() for example returns that 5
>> packets
>> + * have been received, it does not automatically mean that
>> + * xsk_ring_prod__reserve() will have 5 slots available. You
>> will
>> + * see this, for example, when using a veth interface due to
>> the
>> + * RX_BATCH_SIZE used by the generic driver.
>> + *
>> + * In this example we store unused buffers and try to
>> re-stock
>> + * them the next iteration.
>> + */
>> +
>> + free_slots = xsk_prod__nb_free(&xsk->umem->fq, rcvd +
>> nr_free_frames);
>> + if (free_slots > rcvd + nr_free_frames)
>> + free_slots = rcvd + nr_free_frames;
>> +
>> + ret = xsk_ring_prod__reserve(&xsk->umem->fq, free_slots,
>> &idx_fq);
>> + while (ret != free_slots) {
>> if (ret < 0)
>> exit_with_error(-ret);
>> - ret = xsk_ring_prod__reserve(&xsk->umem->fq, rcvd,
>> &idx_fq);
>> + ret = xsk_ring_prod__reserve(&xsk->umem->fq,
>> free_slots,
>> + &idx_fq);
>> }
>>
>> for (i = 0; i < rcvd; i++) {
>> @@ -538,10 +585,22 @@ static void rx_drop(struct xsk_socket_info
>> *xsk)
>> char *pkt = xsk_umem__get_data(xsk->umem->buffer,
>> addr);
>>
>> hex_dump(pkt, len, addr);
>> - *xsk_ring_prod__fill_addr(&xsk->umem->fq, idx_fq++) =
>> addr;
>> + if (i < free_slots)
>> + *xsk_ring_prod__fill_addr(&xsk->umem->fq,
>> idx_fq++) =
>> + addr;
>> + else
>> + free_frames[nr_free_frames++] = addr;
>> + }
>> +
>> + if (free_slots > rcvd) {
>> + for (i = 0; i < (free_slots - rcvd); i++) {
>> + u64 addr = free_frames[--nr_free_frames];
>> + *xsk_ring_prod__fill_addr(&xsk->umem->fq,
>> idx_fq++) =
>> + addr;
>> + }
>> }
>>
>> - xsk_ring_prod__submit(&xsk->umem->fq, rcvd);
>> + xsk_ring_prod__submit(&xsk->umem->fq, free_slots);
>> xsk_ring_cons__release(&xsk->rx, rcvd);
>> xsk->rx_npkts += rcvd;
>> }
>> diff --git a/tools/lib/bpf/xsk.h b/tools/lib/bpf/xsk.h
>> index 833a6e60d065..cae506ab3f3c 100644
>> --- a/tools/lib/bpf/xsk.h
>> +++ b/tools/lib/bpf/xsk.h
>> @@ -76,7 +76,7 @@ xsk_ring_cons__rx_desc(const struct xsk_ring_cons
>> *rx, __u32 idx)
>> return &descs[idx & rx->mask];
>> }
>>
>> -static inline __u32 xsk_prod_nb_free(struct xsk_ring_prod *r, __u32
>> nb)
>> +static inline __u32 xsk_prod__nb_free(struct xsk_ring_prod *r, __u32
>> nb)
>> {
>> __u32 free_entries = r->cached_cons - r->cached_prod;
>>
>> @@ -110,7 +110,7 @@ static inline __u32 xsk_cons_nb_avail(struct
>> xsk_ring_cons *r, __u32 nb)
>> static inline size_t xsk_ring_prod__reserve(struct xsk_ring_prod
>> *prod,
>> size_t nb, __u32 *idx)
>> {
>> - if (xsk_prod_nb_free(prod, nb) < nb)
>> + if (xsk_prod__nb_free(prod, nb) < nb)
>> return 0;
>>
>> *idx = prod->cached_prod;
>> --
>> 2.18.1
>>
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