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Date: Mon, 10 Nov 2014 15:13:08 +0000
From: Bruce Richardson <bruce.richardson@intel.com>
To: Qinglai Xiao <jigsaw@gmail.com>
Message-ID: <20141110151308.GC12532@bricha3-MOBL3>
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Cc: dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH v3] Add in_flight_bitmask so as to use full
32 bits of tag.
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On Mon, Nov 10, 2014 at 04:44:02PM +0200, Qinglai Xiao wrote:
> With introduction of in_flight_bitmask, the whole 32 bits of tag can be
> used. Further more, this patch fixed the integer overflow when finding
> the matched tags.
> The maximum number workers is now defined as 64, which is length of
> double-word. The link between number of workers and RTE_MAX_LCORE is
> now removed. Compile time check is added to ensure the
> RTE_DISTRIB_MAX_WORKERS is less than or equal to size of double-word.
>
> Signed-off-by: Qinglai Xiao <jigsaw@gmail.com>
Looks good to me.
Just before I ack this, have you checked to see if there is any performance impact?
/Bruce
> ---
> lib/librte_distributor/rte_distributor.c | 64 ++++++++++++++++++++++--------
> lib/librte_distributor/rte_distributor.h | 4 ++
> 2 files changed, 51 insertions(+), 17 deletions(-)
>
> diff --git a/lib/librte_distributor/rte_distributor.c b/lib/librte_distributor/rte_distributor.c
> index 3dfec4a..2c5d61c 100644
> --- a/lib/librte_distributor/rte_distributor.c
> +++ b/lib/librte_distributor/rte_distributor.c
> @@ -62,6 +62,13 @@
> #define RTE_DISTRIB_RETURNS_MASK (RTE_DISTRIB_MAX_RETURNS - 1)
>
> /**
> + * Maximum number of workers allowed.
> + * Be aware of increasing the limit, becaus it is limited by how we track
> + * in-flight tags. See @in_flight_bitmask and @rte_distributor_process
> + */
> +#define RTE_DISTRIB_MAX_WORKERS 64
> +
> +/**
> * Buffer structure used to pass the pointer data between cores. This is cache
> * line aligned, but to improve performance and prevent adjacent cache-line
> * prefetches of buffers for other workers, e.g. when worker 1's buffer is on
> @@ -91,11 +98,17 @@ struct rte_distributor {
> char name[RTE_DISTRIBUTOR_NAMESIZE]; /**< Name of the ring. */
> unsigned num_workers; /**< Number of workers polling */
>
> - uint32_t in_flight_tags[RTE_MAX_LCORE];
> - /**< Tracks the tag being processed per core, 0 == no pkt */
> - struct rte_distributor_backlog backlog[RTE_MAX_LCORE];
> + uint32_t in_flight_tags[RTE_DISTRIB_MAX_WORKERS];
> + /**< Tracks the tag being processed per core */
> + uint64_t in_flight_bitmask;
> + /**< on/off bits for in-flight tags.
> + * Note that if RTE_DISTRIB_MAX_WORKERS is larger than 64 then
> + * the bitmask has to expand.
> + */
> +
> + struct rte_distributor_backlog backlog[RTE_DISTRIB_MAX_WORKERS];
>
> - union rte_distributor_buffer bufs[RTE_MAX_LCORE];
> + union rte_distributor_buffer bufs[RTE_DISTRIB_MAX_WORKERS];
>
> struct rte_distributor_returned_pkts returns;
> };
> @@ -189,6 +202,7 @@ static inline void
> handle_worker_shutdown(struct rte_distributor *d, unsigned wkr)
> {
> d->in_flight_tags[wkr] = 0;
> + d->in_flight_bitmask &= ~(1UL << wkr);
> d->bufs[wkr].bufptr64 = 0;
> if (unlikely(d->backlog[wkr].count != 0)) {
> /* On return of a packet, we need to move the
> @@ -211,7 +225,10 @@ handle_worker_shutdown(struct rte_distributor *d, unsigned wkr)
> pkts[i] = (void *)((uintptr_t)(bl->pkts[idx] >>
> RTE_DISTRIB_FLAG_BITS));
> }
> - /* recursive call */
> + /* recursive call.
> + * Note that the tags were set before first level call
> + * to rte_distributor_process.
> + */
> rte_distributor_process(d, pkts, i);
> bl->count = bl->start = 0;
> }
> @@ -242,6 +259,7 @@ process_returns(struct rte_distributor *d)
> else {
> d->bufs[wkr].bufptr64 = RTE_DISTRIB_GET_BUF;
> d->in_flight_tags[wkr] = 0;
> + d->in_flight_bitmask &= ~(1UL << wkr);
> }
> oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
> } else if (data & RTE_DISTRIB_RETURN_BUF) {
> @@ -284,14 +302,18 @@ rte_distributor_process(struct rte_distributor *d,
> next_value = (((int64_t)(uintptr_t)next_mb)
> << RTE_DISTRIB_FLAG_BITS);
> /*
> - * Set the low bit on the tag, so we can guarantee that
> - * we never store a tag value of zero. That means we can
> - * use the zero-value to indicate that no packet is
> - * being processed by a worker.
> + * User is advocated to set tag vaue for each
> + * mbuf before calling rte_distributor_process.
> + * User defined tags are used to identify flows,
> + * or sessions.
> */
> - new_tag = (next_mb->hash.usr | 1);
> + new_tag = next_mb->hash.usr;
>
> - uint32_t match = 0;
> + /*
> + * Note that if RTE_DISTRIB_MAX_WORKERS is larger than 64
> + * then the size of match has to be expanded.
> + */
> + uint64_t match = 0;
> unsigned i;
> /*
> * to scan for a match use "xor" and "not" to get a 0/1
> @@ -303,9 +325,12 @@ rte_distributor_process(struct rte_distributor *d,
> match |= (!(d->in_flight_tags[i] ^ new_tag)
> << i);
>
> + /* Only turned-on bits are considered as match */
> + match &= d->in_flight_bitmask;
> +
> if (match) {
> next_mb = NULL;
> - unsigned worker = __builtin_ctz(match);
> + unsigned worker = __builtin_ctzl(match);
> if (add_to_backlog(&d->backlog[worker],
> next_value) < 0)
> next_idx--;
> @@ -322,6 +347,7 @@ rte_distributor_process(struct rte_distributor *d,
> else {
> d->bufs[wkr].bufptr64 = next_value;
> d->in_flight_tags[wkr] = new_tag;
> + d->in_flight_bitmask |= (1UL << wkr);
> next_mb = NULL;
> }
> oldbuf = data >> RTE_DISTRIB_FLAG_BITS;
> @@ -379,11 +405,13 @@ rte_distributor_returned_pkts(struct rte_distributor *d,
> static inline unsigned
> total_outstanding(const struct rte_distributor *d)
> {
> - unsigned wkr, total_outstanding = 0;
> + unsigned wkr, total_outstanding;
> +
> + total_outstanding = __builtin_popcountl(d->in_flight_bitmask);
>
> for (wkr = 0; wkr < d->num_workers; wkr++)
> - total_outstanding += d->backlog[wkr].count +
> - !!(d->in_flight_tags[wkr]);
> + total_outstanding += d->backlog[wkr].count;
> +
> return total_outstanding;
> }
>
> @@ -423,9 +451,11 @@ rte_distributor_create(const char *name,
>
> /* compilation-time checks */
> RTE_BUILD_BUG_ON((sizeof(*d) & CACHE_LINE_MASK) != 0);
> - RTE_BUILD_BUG_ON((RTE_MAX_LCORE & 7) != 0);
> + RTE_BUILD_BUG_ON((RTE_DISTRIB_MAX_WORKERS & 7) != 0);
> + RTE_BUILD_BUG_ON(RTE_DISTRIB_MAX_WORKERS >
> + sizeof(d->in_flight_bitmask) * CHAR_BIT);
>
> - if (name == NULL || num_workers >= RTE_MAX_LCORE) {
> + if (name == NULL || num_workers >= RTE_DISTRIB_MAX_WORKERS) {
> rte_errno = EINVAL;
> return NULL;
> }
> diff --git a/lib/librte_distributor/rte_distributor.h b/lib/librte_distributor/rte_distributor.h
> index ec0d74a..cc1d559 100644
> --- a/lib/librte_distributor/rte_distributor.h
> +++ b/lib/librte_distributor/rte_distributor.h
> @@ -88,6 +88,10 @@ rte_distributor_create(const char *name, unsigned socket_id,
> * packets. The distributor will ensure that no two packets that have the
> * same flow id, or tag, in the mbuf will be procesed at the same time.
> *
> + * The user is advocated to set tag for each mbuf before calling this function.
> + * If user doesn't set the tag, the tag value can be various values depending on
> + * driver implementation and configuration.
> + *
> * This is not multi-thread safe and should only be called on a single lcore.
> *
> * @param d
> --
> 1.7.1
>