From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [net-next rfc 1/3] net: avoid high order memory allocation for queues by using flex array Date: Wed, 19 Jun 2013 15:22:18 +0300 Message-ID: <20130619122218.GA4990@redhat.com> References: <1371620452-49349-1-git-send-email-jasowang@redhat.com> <1371620452-49349-2-git-send-email-jasowang@redhat.com> <1371623518.3252.267.camel@edumazet-glaptop> <20130619091132.GA2816@redhat.com> <1371635763.3252.289.camel@edumazet-glaptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Jason Wang , davem@davemloft.net, edumazet@google.com, hkchu@google.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org To: Eric Dumazet Return-path: Content-Disposition: inline In-Reply-To: <1371635763.3252.289.camel@edumazet-glaptop> Sender: linux-kernel-owner@vger.kernel.org List-Id: netdev.vger.kernel.org On Wed, Jun 19, 2013 at 02:56:03AM -0700, Eric Dumazet wrote: > On Wed, 2013-06-19 at 12:11 +0300, Michael S. Tsirkin wrote: > > > Well KVM supports up to 160 VCPUs on x86. > > > > Creating a queue per CPU is very reasonable, and > > assuming cache line size of 64 bytes, netdev_queue seems to be 320 > > bytes, that's 320*160 = 51200. So 12.5 pages, order-4 allocation. > > I agree most people don't have such systems yet, but > > they do exist. > > Even so, it will just work, like a fork() is likely to work, even if a > process needs order-1 allocation for kernel stack. > Some drivers still use order-10 allocations with kmalloc(), and nobody > complained yet. > > We had complains with mlx4 driver lately only bcause kmalloc() now gives > a warning if allocations above MAX_ORDER are attempted. > > Having a single pointer means that we can : > > - Attempts a regular kmalloc() call, it will work most of the time. > - fallback to vmalloc() _if_ kmalloc() failed. Most drivers create devices at boot time, when this is more likely to work. What makes tun (and macvlan) a bit special is that the device is created from userspace. Virt setups create/destroy them all the time. > > Frankly, if you want one tx queue per cpu, I would rather use > NETIF_F_LLTX, like some other virtual devices. > > This way, you can have real per cpu memory, with proper NUMA affinity. > Hmm good point, worth looking at. Thanks, -- MST