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From: Bruce Richardson <bruce.richardson@intel.com>
To: "Pai G, Sunil" <sunil.pai.g@intel.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	"Laatz, Kevin" <kevin.laatz@intel.com>,
	"stable@dpdk.org" <stable@dpdk.org>,
	"Hu, Jiayu" <jiayu.hu@intel.com>
Subject: Re: [PATCH] dma/idxd: fix burst capacity calculation
Date: Mon, 10 Jan 2022 13:25:18 +0000	[thread overview]
Message-ID: <YdwzvhBUdCXWJ669@bricha3-MOBL.ger.corp.intel.com> (raw)
In-Reply-To: <DM8PR11MB5605F2B8DFA7B6D84270F9E8BD509@DM8PR11MB5605.namprd11.prod.outlook.com>

On Mon, Jan 10, 2022 at 01:09:02PM +0000, Pai G, Sunil wrote:
> Hi Bruce, Kevin
> 
> This patch seems to have uncovered a bug in the driver.
> On applying, the idxd_burst_capacity API seems to return 0 for cases even when there are batch descriptors and ring space available.
> Seems like there is a wraparound missing when calculating the descriptor ring space, causing this behavior.
> 
> Below change seems to fix the issue.
> 
> @@ -483,7 +496,7 @@ idxd_burst_capacity(const void *dev_private, uint16_t vchan __rte_unused)
>         /* For descriptors, check for wrap-around on write but not read */
>         if (idxd->ids_returned > write_idx)
>                 write_idx += idxd->desc_ring_mask + 1;
> -       used_space = write_idx - idxd->ids_returned;
> +       used_space = (write_idx - idxd->ids_returned)&idxd->desc_ring_mask;
> 
> <snipped>
> 
> Could we include this fix in the current patch ?
>
Hi Sunil,

what values for the write_idx and ids_returned vars give this error, and
how does masking help? I'd expect masking to increase the number of times
the function returns zero, rather than decreasing it.

/Bruce 

  reply	other threads:[~2022-01-10 13:25 UTC|newest]

Thread overview: 17+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-12-20 17:05 Bruce Richardson
2022-01-04 17:16 ` Kevin Laatz
2022-01-05  1:32   ` Hu, Jiayu
2022-01-10 13:09 ` Pai G, Sunil
2022-01-10 13:25   ` Bruce Richardson [this message]
2022-01-10 13:44     ` Pai G, Sunil
2022-01-10 16:18       ` Bruce Richardson
2022-01-11 13:41 ` [PATCH v2 0/4] fixes for dma/idxd Bruce Richardson
2022-01-11 13:41   ` [PATCH v2 1/4] dma/idxd: fix burst capacity calculation Bruce Richardson
2022-01-11 13:41   ` [PATCH v2 2/4] dma/idxd: fix paths to driver sysfs directory Bruce Richardson
2022-01-11 16:50     ` Kevin Laatz
2022-01-11 13:41   ` [PATCH v2 3/4] dma/idxd: fix wrap-around in burst capacity calculation Bruce Richardson
2022-01-11 13:45     ` Pai G, Sunil
2022-01-11 16:50     ` Kevin Laatz
2022-01-11 13:41   ` [PATCH v2 4/4] test_dmadev: increase iterations of capacity test case Bruce Richardson
2022-01-11 16:50     ` Kevin Laatz
2022-01-20 13:06   ` [PATCH v2 0/4] fixes for dma/idxd Thomas Monjalon

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