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Message-ID: <ZBPex400aT1o8CLZ@TONYMAC-ALIBABA.local>
Date: Fri, 17 Mar 2023 11:30:15 +0800
From: Tony Lu <tonylu@...ux.alibaba.com>
To: Kai Shen <KaiShen@...ux.alibaba.com>
Cc: kgraul@...ux.ibm.com, wenjia@...ux.ibm.com, jaka@...ux.ibm.com,
kuba@...nel.org, davem@...emloft.net, netdev@...r.kernel.org,
linux-s390@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [PATCH net-next v5] net/smc: Use percpu ref for wr tx reference
On Fri, Mar 17, 2023 at 03:21:32AM +0000, Kai Shen wrote:
> The refcount wr_tx_refcnt may cause cache thrashing problems among
> cores and we can use percpu ref to mitigate this issue here. We
> gain some performance improvement with percpu ref here on our
> customized smc-r verion. Applying cache alignment may also mitigate
> this problem but it seem more reasonable to use percpu ref here.
> We can also replace wr_reg_refcnt with one percpu reference like
> wr_tx_refcnt.
>
> redis-benchmark on smc-r with atomic wr_tx_refcnt:
> SET: 525707.06 requests per second, p50=0.087 msec
> GET: 554877.38 requests per second, p50=0.087 msec
>
> redis-benchmark on the percpu_ref version:
> SET: 540482.06 requests per second, p50=0.087 msec
> GET: 570711.12 requests per second, p50=0.079 msec
>
> Cases are like "redis-benchmark -h x.x.x.x -q -t set,get -P 1 -n
> 5000000 -c 50 -d 10 --threads 4".
>
> Signed-off-by: Kai Shen <KaiShen@...ux.alibaba.com>
Reviewed-by: Tony Lu <tonylu@...ux.alibaba.com>
> ---
> v1->v2:
> - Modify patch prefix
>
> v2->v3:
> - Make wr_reg_refcnt a percpu one as well
> - Init percpu ref with 0 flag instead of ALLOW_REINIT flag
>
> v3->v4:
> - Update performance data, this data may differ from previous data
> as I ran cases on other machines
>
> v4->v5:
> - Fix patch format
> ---
> net/smc/smc_core.h | 10 ++++++++--
> net/smc/smc_wr.c | 35 ++++++++++++++++++++++++++++-------
> net/smc/smc_wr.h | 5 ++---
> 3 files changed, 38 insertions(+), 12 deletions(-)
>
> diff --git a/net/smc/smc_core.h b/net/smc/smc_core.h
> index 08b457c2d294..1645fba0d2d3 100644
> --- a/net/smc/smc_core.h
> +++ b/net/smc/smc_core.h
> @@ -106,7 +106,10 @@ struct smc_link {
> unsigned long *wr_tx_mask; /* bit mask of used indexes */
> u32 wr_tx_cnt; /* number of WR send buffers */
> wait_queue_head_t wr_tx_wait; /* wait for free WR send buf */
> - atomic_t wr_tx_refcnt; /* tx refs to link */
> + struct {
> + struct percpu_ref wr_tx_refs;
> + } ____cacheline_aligned_in_smp;
> + struct completion tx_ref_comp;
>
> struct smc_wr_buf *wr_rx_bufs; /* WR recv payload buffers */
> struct ib_recv_wr *wr_rx_ibs; /* WR recv meta data */
> @@ -122,7 +125,10 @@ struct smc_link {
>
> struct ib_reg_wr wr_reg; /* WR register memory region */
> wait_queue_head_t wr_reg_wait; /* wait for wr_reg result */
> - atomic_t wr_reg_refcnt; /* reg refs to link */
> + struct {
> + struct percpu_ref wr_reg_refs;
> + } ____cacheline_aligned_in_smp;
> + struct completion reg_ref_comp;
> enum smc_wr_reg_state wr_reg_state; /* state of wr_reg request */
>
> u8 gid[SMC_GID_SIZE];/* gid matching used vlan id*/
> diff --git a/net/smc/smc_wr.c b/net/smc/smc_wr.c
> index b0678a417e09..0021065a600a 100644
> --- a/net/smc/smc_wr.c
> +++ b/net/smc/smc_wr.c
> @@ -377,12 +377,11 @@ int smc_wr_reg_send(struct smc_link *link, struct ib_mr *mr)
> if (rc)
> return rc;
>
> - atomic_inc(&link->wr_reg_refcnt);
> + percpu_ref_get(&link->wr_reg_refs);
> rc = wait_event_interruptible_timeout(link->wr_reg_wait,
> (link->wr_reg_state != POSTED),
> SMC_WR_REG_MR_WAIT_TIME);
> - if (atomic_dec_and_test(&link->wr_reg_refcnt))
> - wake_up_all(&link->wr_reg_wait);
> + percpu_ref_put(&link->wr_reg_refs);
> if (!rc) {
> /* timeout - terminate link */
> smcr_link_down_cond_sched(link);
> @@ -647,8 +646,10 @@ void smc_wr_free_link(struct smc_link *lnk)
> smc_wr_wakeup_tx_wait(lnk);
>
> smc_wr_tx_wait_no_pending_sends(lnk);
> - wait_event(lnk->wr_reg_wait, (!atomic_read(&lnk->wr_reg_refcnt)));
> - wait_event(lnk->wr_tx_wait, (!atomic_read(&lnk->wr_tx_refcnt)));
> + percpu_ref_kill(&lnk->wr_reg_refs);
> + wait_for_completion(&lnk->reg_ref_comp);
> + percpu_ref_kill(&lnk->wr_tx_refs);
> + wait_for_completion(&lnk->tx_ref_comp);
>
> if (lnk->wr_rx_dma_addr) {
> ib_dma_unmap_single(ibdev, lnk->wr_rx_dma_addr,
> @@ -847,6 +848,20 @@ void smc_wr_add_dev(struct smc_ib_device *smcibdev)
> tasklet_setup(&smcibdev->send_tasklet, smc_wr_tx_tasklet_fn);
> }
>
> +static void smcr_wr_tx_refs_free(struct percpu_ref *ref)
> +{
> + struct smc_link *lnk = container_of(ref, struct smc_link, wr_tx_refs);
> +
> + complete(&lnk->tx_ref_comp);
> +}
> +
> +static void smcr_wr_reg_refs_free(struct percpu_ref *ref)
> +{
> + struct smc_link *lnk = container_of(ref, struct smc_link, wr_reg_refs);
> +
> + complete(&lnk->reg_ref_comp);
> +}
> +
> int smc_wr_create_link(struct smc_link *lnk)
> {
> struct ib_device *ibdev = lnk->smcibdev->ibdev;
> @@ -890,9 +905,15 @@ int smc_wr_create_link(struct smc_link *lnk)
> smc_wr_init_sge(lnk);
> bitmap_zero(lnk->wr_tx_mask, SMC_WR_BUF_CNT);
> init_waitqueue_head(&lnk->wr_tx_wait);
> - atomic_set(&lnk->wr_tx_refcnt, 0);
> + rc = percpu_ref_init(&lnk->wr_tx_refs, smcr_wr_tx_refs_free, 0, GFP_KERNEL);
> + if (rc)
> + goto dma_unmap;
> + init_completion(&lnk->tx_ref_comp);
> init_waitqueue_head(&lnk->wr_reg_wait);
> - atomic_set(&lnk->wr_reg_refcnt, 0);
> + rc = percpu_ref_init(&lnk->wr_reg_refs, smcr_wr_reg_refs_free, 0, GFP_KERNEL);
> + if (rc)
> + goto dma_unmap;
> + init_completion(&lnk->reg_ref_comp);
> init_waitqueue_head(&lnk->wr_rx_empty_wait);
> return rc;
>
> diff --git a/net/smc/smc_wr.h b/net/smc/smc_wr.h
> index 45e9b894d3f8..f3008dda222a 100644
> --- a/net/smc/smc_wr.h
> +++ b/net/smc/smc_wr.h
> @@ -63,14 +63,13 @@ static inline bool smc_wr_tx_link_hold(struct smc_link *link)
> {
> if (!smc_link_sendable(link))
> return false;
> - atomic_inc(&link->wr_tx_refcnt);
> + percpu_ref_get(&link->wr_tx_refs);
> return true;
> }
>
> static inline void smc_wr_tx_link_put(struct smc_link *link)
> {
> - if (atomic_dec_and_test(&link->wr_tx_refcnt))
> - wake_up_all(&link->wr_tx_wait);
> + percpu_ref_put(&link->wr_tx_refs);
> }
>
> static inline void smc_wr_drain_cq(struct smc_link *lnk)
> --
> 2.31.1
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