Re: [RFC PATCH net-next v5 05/11] net/smc: implement DMB-related operations of loopback-ism

[Gerd Bayer <gbayer@linux.ibm.com>]

On Sun, 2024-03-24 at 21:55 +0800, Wen Gu wrote:

When I instrumented this to see, why I still see tons of my other
temporary instrumentation messages from the "ism" driver, I found that
in my setup loopback-ism is used rather infrequently.

I suspect this is due to how the SMC proposals are constructed in
net/smc/af_smc.c and net/smc/smc_pnet.c - and later evaluated in
smc_check_ism_v2_match() - where there is a first-come-first-serve
selection.

I wonder if one should change that to favour loopback-ism over "real"
ISM devices - and how this could be achieved elegantly.

Just some food for thought... Probably little you can do on x86.

Thanks,
Gerd

> +static int smc_lo_register_dmb(struct smcd_dev *smcd, struct
> smcd_dmb *dmb,
> +			       void *client_priv)
> +{
> +	struct smc_lo_dmb_node *dmb_node, *tmp_node;
> +	struct smc_lo_dev *ldev = smcd->priv;
> +	int sba_idx, rc;
> +
> +	/* check space for new dmb */
> +	for_each_clear_bit(sba_idx, ldev->sba_idx_mask,
> SMC_LO_MAX_DMBS) {
> +		if (!test_and_set_bit(sba_idx, ldev->sba_idx_mask))
> +			break;
> +	}
> +	if (sba_idx == SMC_LO_MAX_DMBS)
> +		return -ENOSPC;
> +
> +	dmb_node = kzalloc(sizeof(*dmb_node), GFP_KERNEL);
> +	if (!dmb_node) {
> +		rc = -ENOMEM;
> +		goto err_bit;
> +	}
> +
> +	dmb_node->sba_idx = sba_idx;
> +	dmb_node->len = dmb->dmb_len;
> +	dmb_node->cpu_addr = kzalloc(dmb_node->len, GFP_KERNEL |
> +				     __GFP_NOWARN | __GFP_NORETRY |
> +				     __GFP_NOMEMALLOC);
> +	if (!dmb_node->cpu_addr) {
> +		rc = -ENOMEM;
> +		goto err_node;
> +	}
> +	dmb_node->dma_addr = SMC_DMA_ADDR_INVALID;
> +
> +again:
> +	/* add new dmb into hash table */
> +	get_random_bytes(&dmb_node->token, sizeof(dmb_node->token));
> +	write_lock_bh(&ldev->dmb_ht_lock);
> +	hash_for_each_possible(ldev->dmb_ht, tmp_node, list,
> dmb_node->token) {
> +		if (tmp_node->token == dmb_node->token) {
> +			write_unlock_bh(&ldev->dmb_ht_lock);
> +			goto again;
> +		}
> +	}
> +	hash_add(ldev->dmb_ht, &dmb_node->list, dmb_node->token);
> +	write_unlock_bh(&ldev->dmb_ht_lock);
> +
> +	dmb->sba_idx = dmb_node->sba_idx;
> +	dmb->dmb_tok = dmb_node->token;
> +	dmb->cpu_addr = dmb_node->cpu_addr;
> +	dmb->dma_addr = dmb_node->dma_addr;
> +	dmb->dmb_len = dmb_node->len;
> +
> +	return 0;
> +
> +err_node:
> +	kfree(dmb_node);
> +err_bit:
> +	clear_bit(sba_idx, ldev->sba_idx_mask);
> +	return rc;
> +}
> +
> +static int smc_lo_unregister_dmb(struct smcd_dev *smcd, struct
> smcd_dmb *dmb)
> +{
> +	struct smc_lo_dmb_node *dmb_node = NULL, *tmp_node;
> +	struct smc_lo_dev *ldev = smcd->priv;
> +
> +	/* remove dmb from hash table */
> +	write_lock_bh(&ldev->dmb_ht_lock);
> +	hash_for_each_possible(ldev->dmb_ht, tmp_node, list, dmb-
> >dmb_tok) {
> +		if (tmp_node->token == dmb->dmb_tok) {
> +			dmb_node = tmp_node;
> +			break;
> +		}
> +	}
> +	if (!dmb_node) {
> +		write_unlock_bh(&ldev->dmb_ht_lock);
> +		return -EINVAL;
> +	}
> +	hash_del(&dmb_node->list);
> +	write_unlock_bh(&ldev->dmb_ht_lock);
> +
> +	clear_bit(dmb_node->sba_idx, ldev->sba_idx_mask);
> +	kfree(dmb_node->cpu_addr);
> +	kfree(dmb_node);
> +
> +	return 0;
> +}
> +
>  static int smc_lo_add_vlan_id(struct smcd_dev *smcd, u64 vlan_id)
>  {
>  	return -EOPNOTSUPP;
> @@ -75,6 +164,38 @@ static int smc_lo_signal_event(struct smcd_dev
> *dev, struct smcd_gid *rgid,
>  	return 0;
>  }
>  
> +static int smc_lo_move_data(struct smcd_dev *smcd, u64 dmb_tok,
> +			    unsigned int idx, bool sf, unsigned int
> offset,
> +			    void *data, unsigned int size)
> +{
> +	struct smc_lo_dmb_node *rmb_node = NULL, *tmp_node;
> +	struct smc_lo_dev *ldev = smcd->priv;
> +	struct smc_connection *conn;
> +
> +	read_lock_bh(&ldev->dmb_ht_lock);
> +	hash_for_each_possible(ldev->dmb_ht, tmp_node, list,
> dmb_tok) {
> +		if (tmp_node->token == dmb_tok) {
> +			rmb_node = tmp_node;
> +			break;
> +		}
> +	}
> +	if (!rmb_node) {
> +		read_unlock_bh(&ldev->dmb_ht_lock);
> +		return -EINVAL;
> +	}
> +	memcpy((char *)rmb_node->cpu_addr + offset, data, size);
> +	read_unlock_bh(&ldev->dmb_ht_lock);
> +
> +	if (sf) {
> +		conn = smcd->conn[rmb_node->sba_idx];
> +		if (conn && !conn->killed)
> +			tasklet_schedule(&conn->rx_tsklet);
> +		else
> +			return -EPIPE;
> +	}
> +	return 0;
> +}
> +
>  static int smc_lo_supports_v2(void)
>  {
>  	return SMC_LO_V2_CAPABLE;
> @@ -101,14 +222,14 @@ static struct device *smc_lo_get_dev(struct
> smcd_dev *smcd)
>  
>  static const struct smcd_ops lo_ops = {
>  	.query_remote_gid = smc_lo_query_rgid,
> -	.register_dmb		= NULL,
> -	.unregister_dmb		= NULL,
> +	.register_dmb = smc_lo_register_dmb,
> +	.unregister_dmb = smc_lo_unregister_dmb,
>  	.add_vlan_id = smc_lo_add_vlan_id,
>  	.del_vlan_id = smc_lo_del_vlan_id,
>  	.set_vlan_required = smc_lo_set_vlan_required,
>  	.reset_vlan_required = smc_lo_reset_vlan_required,
>  	.signal_event = smc_lo_signal_event,
> -	.move_data		= NULL,
> +	.move_data = smc_lo_move_data,
>  	.supports_v2 = smc_lo_supports_v2,
>  	.get_local_gid = smc_lo_get_local_gid,
>  	.get_chid = smc_lo_get_chid,
> @@ -173,6 +294,8 @@ static void smcd_lo_unregister_dev(struct
> smc_lo_dev *ldev)
>  static int smc_lo_dev_init(struct smc_lo_dev *ldev)
>  {
>  	smc_lo_generate_ids(ldev);
> +	rwlock_init(&ldev->dmb_ht_lock);
> +	hash_init(ldev->dmb_ht);
>  	return smcd_lo_register_dev(ldev);
>  }
>  
> diff --git a/net/smc/smc_loopback.h b/net/smc/smc_loopback.h
> index 11868e5ac732..6c4a390430f3 100644
> --- a/net/smc/smc_loopback.h
> +++ b/net/smc/smc_loopback.h
> @@ -20,13 +20,26 @@
>  
>  #if IS_ENABLED(CONFIG_SMC_LO)
>  #define SMC_LO_MAX_DMBS		5000
> +#define SMC_LO_DMBS_HASH_BITS	12
>  #define SMC_LO_RESERVED_CHID	0xFFFF
>  
> +struct smc_lo_dmb_node {
> +	struct hlist_node list;
> +	u64 token;
> +	u32 len;
> +	u32 sba_idx;
> +	void *cpu_addr;
> +	dma_addr_t dma_addr;
> +};
> +
>  struct smc_lo_dev {
>  	struct smcd_dev *smcd;
>  	struct device dev;
>  	u16 chid;
>  	struct smcd_gid local_gid;
> +	rwlock_t dmb_ht_lock;
> +	DECLARE_BITMAP(sba_idx_mask, SMC_LO_MAX_DMBS);
> +	DECLARE_HASHTABLE(dmb_ht, SMC_LO_DMBS_HASH_BITS);
>  };
>  #endif
>