Re: [dpdk-dev] [21.08 PATCH v1 1/2] power: invert the monitor check

["Liu, Yong" <yong.liu@intel.com>]

> -----Original Message-----
> From: dev <dev-bounces@dpdk.org> On Behalf Of Anatoly Burakov
> Sent: Tuesday, May 11, 2021 11:32 PM
> To: dev@dpdk.org; McDaniel, Timothy <timothy.mcdaniel@intel.com>; Xing,
> Beilei <beilei.xing@intel.com>; Wu, Jingjing <jingjing.wu@intel.com>; Yang,
> Qiming <qiming.yang@intel.com>; Zhang, Qi Z <qi.z.zhang@intel.com>;
> Wang, Haiyue <haiyue.wang@intel.com>; Matan Azrad
> <matan@nvidia.com>; Shahaf Shuler <shahafs@nvidia.com>; Viacheslav
> Ovsiienko <viacheslavo@nvidia.com>; Richardson, Bruce
> <bruce.richardson@intel.com>; Ananyev, Konstantin
> <konstantin.ananyev@intel.com>
> Cc: Loftus, Ciara <ciara.loftus@intel.com>
> Subject: [dpdk-dev] [21.08 PATCH v1 1/2] power: invert the monitor check
> 
> Previously, the semantics of power monitor were such that we were
> checking current value against the expected value, and if they matched,
> then the sleep was aborted. This is somewhat inflexible, because it only
> allowed us to check for a specific value.
> 
> We can reverse the check, and instead have monitor sleep to be aborted
> if the expected value *doesn't* match what's in memory. This allows us
> to both implement all currently implemented driver code, as well as
> support more use cases which don't easily map to previous semantics
> (such as waiting on writes to AF_XDP counter value).
> 

Hi Anatoly,
In virtio spec, packed formatted descriptor utilizes two bits for representing the status. One bit for available status, one bit for used status. 
For checking the status more precisely, it is need to check value against the expected value. 
The monitor function in virtio datapath still can work with new semantics, but it may lead to some useless io call. 
Base on that, I'd like to keep previous semantics.

Regards,
Marvin

> This commit also adjusts all current driver implementations to match the
> new semantics.
> 
> Signed-off-by: Anatoly Burakov <anatoly.burakov@intel.com>
> ---
>  drivers/event/dlb2/dlb2.c                      | 2 +-
>  drivers/net/i40e/i40e_rxtx.c                   | 2 +-
>  drivers/net/iavf/iavf_rxtx.c                   | 2 +-
>  drivers/net/ice/ice_rxtx.c                     | 2 +-
>  drivers/net/ixgbe/ixgbe_rxtx.c                 | 2 +-
>  drivers/net/mlx5/mlx5_rx.c                     | 2 +-
>  lib/eal/include/generic/rte_power_intrinsics.h | 8 ++++----
>  lib/eal/x86/rte_power_intrinsics.c             | 4 ++--
>  8 files changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/event/dlb2/dlb2.c b/drivers/event/dlb2/dlb2.c
> index 3570678b9e..5701bbb8ab 100644
> --- a/drivers/event/dlb2/dlb2.c
> +++ b/drivers/event/dlb2/dlb2.c
> @@ -3188,7 +3188,7 @@ dlb2_dequeue_wait(struct dlb2_eventdev *dlb2,
>  			&cq_base[qm_port->cq_idx];
>  		monitor_addr++; /* cq_gen bit is in second 64bit location */
> 
> -		if (qm_port->gen_bit)
> +		if (!qm_port->gen_bit)
>  			expected_value = qe_mask.raw_qe[1];
>  		else
>  			expected_value = 0;
> diff --git a/drivers/net/i40e/i40e_rxtx.c b/drivers/net/i40e/i40e_rxtx.c
> index 02cf5e787c..4617ae914a 100644
> --- a/drivers/net/i40e/i40e_rxtx.c
> +++ b/drivers/net/i40e/i40e_rxtx.c
> @@ -88,7 +88,7 @@ i40e_get_monitor_addr(void *rx_queue, struct
> rte_power_monitor_cond *pmc)
>  	 * we expect the DD bit to be set to 1 if this descriptor was already
>  	 * written to.
>  	 */
> -	pmc->val = rte_cpu_to_le_64(1 << I40E_RX_DESC_STATUS_DD_SHIFT);
> +	pmc->val = 0;
>  	pmc->mask = rte_cpu_to_le_64(1 <<
> I40E_RX_DESC_STATUS_DD_SHIFT);
> 
>  	/* registers are 64-bit */
> diff --git a/drivers/net/iavf/iavf_rxtx.c b/drivers/net/iavf/iavf_rxtx.c
> index 87f7eebc65..d8d9cc860c 100644
> --- a/drivers/net/iavf/iavf_rxtx.c
> +++ b/drivers/net/iavf/iavf_rxtx.c
> @@ -73,7 +73,7 @@ iavf_get_monitor_addr(void *rx_queue, struct
> rte_power_monitor_cond *pmc)
>  	 * we expect the DD bit to be set to 1 if this descriptor was already
>  	 * written to.
>  	 */
> -	pmc->val = rte_cpu_to_le_64(1 <<
> IAVF_RX_DESC_STATUS_DD_SHIFT);
> +	pmc->val = 0;
>  	pmc->mask = rte_cpu_to_le_64(1 <<
> IAVF_RX_DESC_STATUS_DD_SHIFT);
> 
>  	/* registers are 64-bit */
> diff --git a/drivers/net/ice/ice_rxtx.c b/drivers/net/ice/ice_rxtx.c
> index 92fbbc18da..4e349bfa3f 100644
> --- a/drivers/net/ice/ice_rxtx.c
> +++ b/drivers/net/ice/ice_rxtx.c
> @@ -43,7 +43,7 @@ ice_get_monitor_addr(void *rx_queue, struct
> rte_power_monitor_cond *pmc)
>  	 * we expect the DD bit to be set to 1 if this descriptor was already
>  	 * written to.
>  	 */
> -	pmc->val = rte_cpu_to_le_16(1 <<
> ICE_RX_FLEX_DESC_STATUS0_DD_S);
> +	pmc->val = 0;
>  	pmc->mask = rte_cpu_to_le_16(1 <<
> ICE_RX_FLEX_DESC_STATUS0_DD_S);
> 
>  	/* register is 16-bit */
> diff --git a/drivers/net/ixgbe/ixgbe_rxtx.c b/drivers/net/ixgbe/ixgbe_rxtx.c
> index d69f36e977..2793718171 100644
> --- a/drivers/net/ixgbe/ixgbe_rxtx.c
> +++ b/drivers/net/ixgbe/ixgbe_rxtx.c
> @@ -1385,7 +1385,7 @@ ixgbe_get_monitor_addr(void *rx_queue, struct
> rte_power_monitor_cond *pmc)
>  	 * we expect the DD bit to be set to 1 if this descriptor was already
>  	 * written to.
>  	 */
> -	pmc->val = rte_cpu_to_le_32(IXGBE_RXDADV_STAT_DD);
> +	pmc->val = 0;
>  	pmc->mask = rte_cpu_to_le_32(IXGBE_RXDADV_STAT_DD);
> 
>  	/* the registers are 32-bit */
> diff --git a/drivers/net/mlx5/mlx5_rx.c b/drivers/net/mlx5/mlx5_rx.c
> index 6cd71a44eb..3cbbe5bf59 100644
> --- a/drivers/net/mlx5/mlx5_rx.c
> +++ b/drivers/net/mlx5/mlx5_rx.c
> @@ -282,7 +282,7 @@ int mlx5_get_monitor_addr(void *rx_queue, struct
> rte_power_monitor_cond *pmc)
>  		return -rte_errno;
>  	}
>  	pmc->addr = &cqe->op_own;
> -	pmc->val =  !!idx;
> +	pmc->val =  !idx;
>  	pmc->mask = MLX5_CQE_OWNER_MASK;
>  	pmc->size = sizeof(uint8_t);
>  	return 0;
> diff --git a/lib/eal/include/generic/rte_power_intrinsics.h
> b/lib/eal/include/generic/rte_power_intrinsics.h
> index dddca3d41c..28c481a8d2 100644
> --- a/lib/eal/include/generic/rte_power_intrinsics.h
> +++ b/lib/eal/include/generic/rte_power_intrinsics.h
> @@ -45,10 +45,10 @@ struct rte_power_monitor_cond {
>   * Additionally, an expected value (`pmc->val`), mask (`pmc->mask`), and
> data
>   * size (`pmc->size`) are provided in the `pmc` power monitoring condition. If
>   * the mask is non-zero, the current value pointed to by the `pmc->addr`
> pointer
> - * will be read and compared against the expected value, and if they match,
> the
> - * entering of optimized power state will be aborted. This is intended to
> - * prevent the CPU from entering optimized power state and waiting on a
> write
> - * that has already happened by the time this API is called.
> + * will be read and compared against the expected value, and if they do not
> + * match, the entering of optimized power state will be aborted. This is
> + * intended to prevent the CPU from entering optimized power state and
> waiting
> + * on a write that has already happened by the time this API is called.
>   *
>   * @warning It is responsibility of the user to check if this function is
>   *   supported at runtime using `rte_cpu_get_intrinsics_support()` API call.
> diff --git a/lib/eal/x86/rte_power_intrinsics.c
> b/lib/eal/x86/rte_power_intrinsics.c
> index 39ea9fdecd..7f0588d70e 100644
> --- a/lib/eal/x86/rte_power_intrinsics.c
> +++ b/lib/eal/x86/rte_power_intrinsics.c
> @@ -116,8 +116,8 @@ rte_power_monitor(const struct
> rte_power_monitor_cond *pmc,
>  				pmc->addr, pmc->size);
>  		const uint64_t masked = cur_value & pmc->mask;
> 
> -		/* if the masked value is already matching, abort */
> -		if (masked == pmc->val)
> +		/* if the masked value is not matching, abort */
> +		if (masked != pmc->val)
>  			goto end;
>  	}
> 
> --
> 2.25.1