From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [RFC 2/4] tuntap: Publish tuntap maximum number of queues as module_param Date: Wed, 20 Aug 2014 13:49:07 +0200 Message-ID: <20140820114907.GA17943@redhat.com> References: <1408369040-1216-1-git-send-email-pagupta@redhat.com> <1408369040-1216-3-git-send-email-pagupta@redhat.com> <20140820105817.GB1916@nanopsycho.orion> <20140820111724.GE17371@redhat.com> <20140820114620.GC1916@nanopsycho.orion> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Pankaj Gupta , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, davem@davemloft.net, jasowang@redhat.com, dgibson@redhat.com, vfalico@gmail.com, edumazet@google.com, vyasevic@redhat.com, hkchu@google.com, wuzhy@linux.vnet.ibm.com, xemul@parallels.com, therbert@google.com, bhutchings@solarflare.com, xii@google.com, stephen@networkplumber.org To: Jiri Pirko Return-path: Content-Disposition: inline In-Reply-To: <20140820114620.GC1916@nanopsycho.orion> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Aug 20, 2014 at 01:46:20PM +0200, Jiri Pirko wrote: > Wed, Aug 20, 2014 at 01:17:24PM CEST, mst@redhat.com wrote: > >On Wed, Aug 20, 2014 at 12:58:17PM +0200, Jiri Pirko wrote: > >> Mon, Aug 18, 2014 at 03:37:18PM CEST, pagupta@redhat.com wrote: > >> > This patch publishes maximum number of tun/tap queues allocated as a > >> > read_only module parameter which a user space application like libvirt > >> > can make use of to limit maximum number of queues. Value of read_only > >> > module parameter can be writable only at module load time. If no value is set > >> > at module load time a default value 256 is used which is equal to maximum number > >> > of vCPUS allowed by KVM. > >> > > >> > Administrator can specify maximum number of queues only at the driver > >> > module load time. > >> > > >> >Signed-off-by: Pankaj Gupta > >> >--- > >> > drivers/net/tun.c | 13 +++++++++++-- > >> > 1 files changed, 11 insertions(+), 2 deletions(-) > >> > > >> >diff --git a/drivers/net/tun.c b/drivers/net/tun.c > >> >index acaaf67..1f518e2 100644 > >> >--- a/drivers/net/tun.c > >> >+++ b/drivers/net/tun.c > >> >@@ -119,6 +119,9 @@ struct tap_filter { > >> > > >> > #define TUN_FLOW_EXPIRE (3 * HZ) > >> > > >> >+static int max_tap_queues = MAX_TAP_QUEUES; > >> >+module_param(max_tap_queues, int, S_IRUGO); > >> > >> Please do not introduce new module paramaters. Please other ways to > >> interchange values with userspace. > > > >I suggested this initially, but thinking more about it, I agree. > > > >It's a global limit (necessary to limit memory utilization by > >userspace), but it should be possible to change it > >after module load. > > > >Additionally, userspace that has the FD should be able to > >retrieve the value without guessing that the FD is > >for the tun device (and not e.g. macvtap). > >To retrieve the value, an ioctl is probably the > >cleanest approach. > > > >To set it, how about a sysctl? I think the limit can also apply to > >all devices, not just tun. > > Or netlink? Are there examples of netlink being used to set global defaults as opposed to per-device parameters? > > > >-- > >MST