Re: [PATCH] Adding RTE_KNI_PREEMPT configuration option

[Bruce Richardson <bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>]

On Wed, Feb 11, 2015 at 01:26:41PM +0100, Marc Sune wrote:
> 
> On 11/02/15 02:54, Zhang, Helin wrote:
> >
> >>-----Original Message-----
> >>From: Richardson, Bruce
> >>Sent: Tuesday, February 10, 2015 9:24 PM
> >>To: Marc Sune
> >>Cc: dev-VfR2kkLFssw@public.gmane.org; Zhang, Helin
> >>Subject: Re: [dpdk-dev] [PATCH] Adding RTE_KNI_PREEMPT configuration
> >>option
> >>
> >>On Tue, Feb 10, 2015 at 12:59:29PM +0100, Marc Sune wrote:
> >>>This patch of Nov 2014 hasn't been yet ACKed/NACKed. Could someone
> >>>please give some quick feedback?
> >>>
> >>>Thanks
> >>>marc
> >>>
> >>>On 07/11/14 12:00, Marc Sune wrote:
> >>>>This patch introduces CONFIG_RTE_KNI_PREEMPT flag. When set to 'no',
> >>>>KNI kernel thread(s) do not call schedule_timeout_interruptible(),
> >>>>which improves overall KNI performance at the expense of CPU cycles
> >>(polling).
> >>>>Default values is 'yes', maintaining the same behaviour as of now.
> >>>>
> >>>>Signed-off-by: Marc Sune <marc.sune-kpkqNMk1I7M@public.gmane.org>
> >>Although a better option would be to have a runtime setting, this is still an
> >>improvement over what we have.
> >>
> >>Acked-by: Bruce Richardson <bruce.richardson-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
> >>
> >>>>---
> >>>>  config/common_linuxapp                 |    1 +
> >>>>  lib/librte_eal/linuxapp/kni/kni_misc.c |    4 ++++
> >>>>  2 files changed, 5 insertions(+)
> >>>>
> >>>>diff --git a/config/common_linuxapp b/config/common_linuxapp index
> >>>>57b61c9..24b529d 100644
> >>>>--- a/config/common_linuxapp
> >>>>+++ b/config/common_linuxapp
> >>>>@@ -380,6 +380,7 @@ CONFIG_RTE_LIBRTE_PIPELINE=y
> >>>>  # Compile librte_kni
> >>>>  #
> >>>>  CONFIG_RTE_LIBRTE_KNI=y
> >>>>+CONFIG_RTE_KNI_PREEMPT=y
> >>>>  CONFIG_RTE_KNI_KO_DEBUG=n
> >>>>  CONFIG_RTE_KNI_VHOST=n
> >>>>  CONFIG_RTE_KNI_VHOST_MAX_CACHE_SIZE=1024
> >>>>diff --git a/lib/librte_eal/linuxapp/kni/kni_misc.c
> >>>>b/lib/librte_eal/linuxapp/kni/kni_misc.c
> >>>>index ba77776..e7e6c27 100644
> >>>>--- a/lib/librte_eal/linuxapp/kni/kni_misc.c
> >>>>+++ b/lib/librte_eal/linuxapp/kni/kni_misc.c
> >>>>@@ -229,9 +229,11 @@ kni_thread_single(void *unused)
> >>>>  			}
> >>>>  		}
> >>>>  		up_read(&kni_list_lock);
> >>>>+#ifdef RTE_KNI_PREEMPT
> >>>>  		/* reschedule out for a while */
> >>>>  		schedule_timeout_interruptible(usecs_to_jiffies( \
> >>>>  				KNI_KTHREAD_RESCHEDULE_INTERVAL));
> >>>>+#endif
> >>>>  	}
> >>>>  	return 0;
> >>>>@@ -252,8 +254,10 @@ kni_thread_multiple(void *param)
> >>>>  #endif
> >>>>  			kni_net_poll_resp(dev);
> >>>>  		}
> >>>>+#ifdef RTE_KNI_PREEMPT
> >>>>  		schedule_timeout_interruptible(usecs_to_jiffies( \
> >>>>  				KNI_KTHREAD_RESCHEDULE_INTERVAL));
> >>>>+#endif
> >>>>  	}
> >>>>  	return 0;
> >As Bruce indicated, it would be better to do that at runtime, we can
> >add a config in struct rte_kni_conf, which will be copied to
> >struct rte_kni_device_info, then kernel space will know the configuration.
> >This way, we can enable/disable PREEMPT during KNI instance allocation time.
> 
> As I said before, I see the point on having it at runtime and I agree.
> 
> However, rte_kni_device_info is a struct that is per interface, not for the
> entire KNI subsystem, so it is kind of abusing to add a flag there when only
> will be used once, at bootstrap. To do it "properly" we should create a new
> ioctl() call IMHO.
> 
> >Anyway, it can be done now or later.
> 
> So, do we integrate the current patch, as acked by Bruce before?
> 
> Marc

I'd like to see it go in, as a step forward, rather than not having it at all
because it's not quite perfect.

One suggestion might be to have the compile time setting be
"CONFIG_RTE_KNI_PREEMPT_DEFAULT" rather than just "CONFIG_RTE_KNI_PREEMPT". This
would mean that we would not need to remove the setting later if we do add a
runtime option, as the setting only specified the default value rather than
the final value. :-)

/Bruce