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

["Rafał Kozik" <rk@semihalf.com>]

2018-06-29 11:05 GMT+02:00 Ferruh Yigit <ferruh.yigit@intel.com>:
> On 6/29/2018 9:58 AM, Rafał Kozik wrote:
>> 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.
>
> OK, perhaps not error log to prevent mislead, but what do you think "info" level
> log, to notify the user that write combined version in not used.
>

In new revision of patch set I add logging of device name.
For every resources it provides information if mapped with or without WC.

It looks like:
EAL: /sys/bus/pci/devices/0000:00:06.0/resource0 mapped
EAL: /sys/bus/pci/devices/0000:00:06.0/resource2_wc mapped
EAL: /sys/bus/pci/devices/0000:00:06.0/resource4 mapped

>>
>>>> +     }
>>>> +
>>>> +     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 */
>>>>
>>>
>