Re: [dpdk-dev] [PATCH v3 1/1] bus/pci: optimise scanning with whitelist/blacklist

["Gaëtan Rivet" <grive@u256.net>]

Hello Sunil,

As it seems that this patch does not overly alarm people using the PCI
bus, I have a few comments on this version. Sending those a little
earlier will allow you to change as needed before proceeding with your
tests.

On 20/04/20 12:25 +0530, Sunil Kumar Kori wrote:
> rte_bus_scan API scans all the available PCI devices irrespective of white
> or black listing parameters then further devices are probed based on white
> or black listing parameters. So unnecessary CPU cycles are wasted during
> rte_pci_scan.
> 
> For Octeontx2 platform with core frequency 2.4 Ghz, rte_bus_scan consumes
> around 26ms to scan around 90 PCI devices but all may not be used by the
> application. So for the application which uses 2 NICs, rte_bus_scan
> consumes few microseconds and rest time is saved with this patch.
> 
> Patch restricts devices to be scanned as per below mentioned conditions:
>  - All devices will be scanned if no parameters are passed.
>  - Only white listed devices will be scanned if white list is available.
>  - All devices, except black listed, will be scanned if black list is
>    available.
> 
> Signed-off-by: Sunil Kumar Kori <skori@marvell.com>
> ---
> v3:
>  - remove __rte_experimental from private function.
>  - remove entry from map file too.
> v2:
>  - Added function to validate ignorance of device based on PCI address.
>  - Marked device validation function as experimental.
> 
>  drivers/bus/pci/bsd/pci.c    | 13 ++++++++++++-
>  drivers/bus/pci/linux/pci.c  |  3 +++
>  drivers/bus/pci/pci_common.c | 34 ++++++++++++++++++++++++++++++++++
>  drivers/bus/pci/private.h    | 11 +++++++++++
>  4 files changed, 60 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/pci/bsd/pci.c b/drivers/bus/pci/bsd/pci.c
> index ebbfeb13a..c8d954751 100644
> --- a/drivers/bus/pci/bsd/pci.c
> +++ b/drivers/bus/pci/bsd/pci.c
> @@ -338,6 +338,7 @@ rte_pci_scan(void)
>  			.match_buf_len = sizeof(matches),
>  			.matches = &matches[0],
>  	};
> +	struct rte_pci_addr pci_addr;
>  
>  	/* for debug purposes, PCI can be disabled */
>  	if (!rte_eal_has_pci())
> @@ -357,9 +358,19 @@ rte_pci_scan(void)
>  			goto error;
>  		}
>  
> -		for (i = 0; i < conf_io.num_matches; i++)
> +		for (i = 0; i < conf_io.num_matches; i++) {
> +			pci_addr.domain = matches[i].pc_sel.pc_domain;
> +			pci_addr.bus = matches[i].pc_sel.pc_bus;
> +			pci_addr.devid = matches[i].pc_sel.pc_dev;
> +			pci_addr.function = matches[i].pc_sel.pc_func;
> +
> +			/* Check that device should be ignored or not  */

This comment is unnecessary, the function name should be sufficient to
describe the check done.

> +			if (pci_addr_ignore_device(&pci_addr))
> +				continue;
> +

As this function is almost a copy of pci_ignore_device(), with a twist
on the addr, I think the name pci_ignore_device_addr() would be more
helpful.

I think in general however, that exposed symbols, even internals,
should be prefixed with rte_. It was (almost) ok for
pci_ignore_device() to forego the namespace as it is a static function
that will be mangled on export, but that won't be the case for your
function.

Please add rte_ prefix.

>  			if (pci_scan_one(fd, &matches[i]) < 0)
>  				goto error;
> +		}
>  
>  		dev_count += conf_io.num_matches;
>  	} while(conf_io.status == PCI_GETCONF_MORE_DEVS);
> diff --git a/drivers/bus/pci/linux/pci.c b/drivers/bus/pci/linux/pci.c
> index 71b0a3053..92bdad826 100644
> --- a/drivers/bus/pci/linux/pci.c
> +++ b/drivers/bus/pci/linux/pci.c
> @@ -487,6 +487,9 @@ rte_pci_scan(void)
>  		if (parse_pci_addr_format(e->d_name, sizeof(e->d_name), &addr) != 0)
>  			continue;
>  
> +		if (pci_addr_ignore_device(&addr))
> +			continue;
> +
>  		snprintf(dirname, sizeof(dirname), "%s/%s",
>  				rte_pci_get_sysfs_path(), e->d_name);
>  
> diff --git a/drivers/bus/pci/pci_common.c b/drivers/bus/pci/pci_common.c
> index 3f5542076..a350a1993 100644
> --- a/drivers/bus/pci/pci_common.c
> +++ b/drivers/bus/pci/pci_common.c
> @@ -589,6 +589,40 @@ pci_dma_unmap(struct rte_device *dev, void *addr, uint64_t iova, size_t len)
>  	return -1;
>  }
>  
> +static struct rte_devargs *
> +pci_addr_devargs_lookup(const struct rte_pci_addr *pci_addr)
> +{
> +	struct rte_devargs *devargs;
> +	struct rte_pci_addr addr;
> +
> +	RTE_EAL_DEVARGS_FOREACH("pci", devargs) {
> +		devargs->bus->parse(devargs->name, &addr);

Why not use rte_pci_addr_parse directly there? The bus->parse() API,
while stable, is one-level of indirection removed from what's done,
it's simpler for the reader to see the intent by using the proper function.

Return value should be checked. If the devargs name is not parseable,
there are other issues at hand (memory corruption), we should skip the
device as well or crash, but not proceed with comparison.

> +		if (!rte_pci_addr_cmp(pci_addr, &addr))
> +			return devargs;
> +	}
> +	return NULL;
> +}
> +
> +bool
> +pci_addr_ignore_device(const struct rte_pci_addr *pci_addr)
> +{
> +	struct rte_devargs *devargs = pci_addr_devargs_lookup(pci_addr);
> +
> +	switch (rte_pci_bus.bus.conf.scan_mode) {
> +	case RTE_BUS_SCAN_WHITELIST:
> +		if (devargs && devargs->policy == RTE_DEV_WHITELISTED)
> +			return false;
> +		break;
> +	case RTE_BUS_SCAN_UNDEFINED:
> +	case RTE_BUS_SCAN_BLACKLIST:
> +		if (devargs == NULL ||
> +		    devargs->policy != RTE_DEV_BLACKLISTED)
> +			return false;
> +		break;
> +	}
> +	return true;
> +}
> +
>  static bool
>  pci_ignore_device(const struct rte_pci_device *dev)
>  {

The logic seems ok to me.

However, the logic is the same as the one in rte_pci_probe(). During
probe, any device on the bus would have already been vetted during scan.
It should be ok to probe all existing rte_pci_device.

The same argument can be made for rte_pci_get_iommu_class() then, no
need to use pci_ignore_device(). It is done after the scan() so it
should be ok.

And if pci_ignore_device() can be completely removed, then you should
rename your function from rte_pci_ignore_device_addr() to
rte_pci_ignore_device() altogether.

> diff --git a/drivers/bus/pci/private.h b/drivers/bus/pci/private.h
> index a205d4d9f..75af786f7 100644
> --- a/drivers/bus/pci/private.h
> +++ b/drivers/bus/pci/private.h
> @@ -42,6 +42,17 @@ int rte_pci_scan(void);
>  void
>  pci_name_set(struct rte_pci_device *dev);
>  
> +/**
> + * Validate whether a device with given pci address should be ignored or not.
> + *
> + * @param pci_addr
> + *	PCI address of device to be validated
> + * @return
> + *	1: if device is to be ignored,
> + *	0: if device is to be scanned,
> + */
> +bool pci_addr_ignore_device(const struct rte_pci_addr *pci_addr);
> +
>  /**
>   * Add a PCI device to the PCI Bus (append to PCI Device list). This function
>   * also updates the bus references of the PCI Device (and the generic device
> -- 
> 2.17.1

Best regards,
-- 
Gaëtan