Re: [dpdk-dev] [PATCH v2 3/4] eal: enable WC during resources mapping

["Rafał Kozik" <rk@semihalf.com>]

2018-06-28 16:50 GMT+02:00 Ferruh Yigit <ferruh.yigit@intel.com>:
> On 6/28/2018 2:15 PM, Rafal Kozik wrote:
>> Write combining (WC) increases NIC performance by making better
>> utilization of PCI bus, but cannot be used by all PMDs.
>>
>> It will be enabled only if RTE_PCI_DRV_WC_ACTIVATE will be set in
>> drivers flags. For proper work also igb_uio driver must be loaded with
>> wc_activate set to 1.
>>
>> When mapping PCI resources, firstly try to us WC.
>> If it is not supported it will fallback to normal mode.
>>
>> Signed-off-by: Rafal Kozik <rk@semihalf.com>
>> Acked-by: Bruce Richardson <bruce.richardson@intel.com>
>> ---
>>  drivers/bus/pci/linux/pci_uio.c | 41 +++++++++++++++++++++++++++++------------
>>  drivers/bus/pci/rte_bus_pci.h   |  2 ++
>>  2 files changed, 31 insertions(+), 12 deletions(-)
>>
>> diff --git a/drivers/bus/pci/linux/pci_uio.c b/drivers/bus/pci/linux/pci_uio.c
>> index d423e4b..e3947c2 100644
>> --- a/drivers/bus/pci/linux/pci_uio.c
>> +++ b/drivers/bus/pci/linux/pci_uio.c
>> @@ -282,22 +282,19 @@ int
>>  pci_uio_map_resource_by_index(struct rte_pci_device *dev, int res_idx,
>>               struct mapped_pci_resource *uio_res, int map_idx)
>>  {
>> -     int fd;
>> +     int fd = -1;
>>       char devname[PATH_MAX];
>>       void *mapaddr;
>>       struct rte_pci_addr *loc;
>>       struct pci_map *maps;
>> +     int wc_activate = 0;
>> +
>> +     if (dev->driver != NULL)
>> +             wc_activate = dev->driver->drv_flags & RTE_PCI_DRV_WC_ACTIVATE;
>>
>>       loc = &dev->addr;
>>       maps = uio_res->maps;
>>
>> -     /* update devname for mmap  */
>> -     snprintf(devname, sizeof(devname),
>> -                     "%s/" PCI_PRI_FMT "/resource%d",
>> -                     rte_pci_get_sysfs_path(),
>> -                     loc->domain, loc->bus, loc->devid,
>> -                     loc->function, res_idx);
>> -
>>       /* allocate memory to keep path */
>>       maps[map_idx].path = rte_malloc(NULL, strlen(devname) + 1, 0);
>>       if (maps[map_idx].path == NULL) {
>> @@ -309,11 +306,31 @@ pci_uio_map_resource_by_index(struct rte_pci_device *dev, int res_idx,
>>       /*
>>        * open resource file, to mmap it
>>        */
>> -     fd = open(devname, O_RDWR);
>> -     if (fd < 0) {
>> -             RTE_LOG(ERR, EAL, "Cannot open %s: %s\n",
>> +     if (wc_activate) {
>> +             /* update devname for mmap  */
>> +             snprintf(devname, sizeof(devname),
>> +                     "%s/" PCI_PRI_FMT "/resource%d_wc",
>> +                     rte_pci_get_sysfs_path(),
>> +                     loc->domain, loc->bus, loc->devid,
>> +                     loc->function, res_idx);
>> +
>> +             fd = open(devname, O_RDWR);
>
> What do you think adding an error log here? If opening resource$_wc fails and
> fallback to resource# file, there won't be any way for user to know about it.
>

This error will be misleading for two reasons:
 * even if open return success, it could silently fall-back to non
prefetchable mode,
 * NICs could have multiple BARs, but not all support WC. I such case
fails will be desirable.

>> +     }
>> +
>> +     if (!wc_activate || fd < 0) {
>> +             snprintf(devname, sizeof(devname),
>> +                     "%s/" PCI_PRI_FMT "/resource%d",
>> +                     rte_pci_get_sysfs_path(),
>> +                     loc->domain, loc->bus, loc->devid,
>> +                     loc->function, res_idx);
>> +
>> +             /* then try to map resource file */
>> +             fd = open(devname, O_RDWR);
>> +             if (fd < 0) {
>> +                     RTE_LOG(ERR, EAL, "Cannot open %s: %s\n",
>>                               devname, strerror(errno));
>> -             goto error;
>> +                     goto error;
>> +             }
>>       }
>>
>>       /* try mapping somewhere close to the end of hugepages */
>> diff --git a/drivers/bus/pci/rte_bus_pci.h b/drivers/bus/pci/rte_bus_pci.h
>> index 458e6d0..828acc5 100644
>> --- a/drivers/bus/pci/rte_bus_pci.h
>> +++ b/drivers/bus/pci/rte_bus_pci.h
>> @@ -135,6 +135,8 @@ struct rte_pci_bus {
>>
>>  /** Device needs PCI BAR mapping (done with either IGB_UIO or VFIO) */
>>  #define RTE_PCI_DRV_NEED_MAPPING 0x0001
>> +/** Device needs PCI BAR mapping with enabled write combining (wc) */
>> +#define RTE_PCI_DRV_WC_ACTIVATE 0x0002
>>  /** Device driver supports link state interrupt */
>>  #define RTE_PCI_DRV_INTR_LSC 0x0008
>>  /** Device driver supports device removal interrupt */
>>
>