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Message-ID: <20120831095628.GB24244@redhat.com> Date: Fri, 31 Aug 2012 12:56:28 +0300 From: "Michael S. Tsirkin" <mst@...hat.com> To: Sasha Levin <levinsasha928@...il.com> Cc: rusty@...tcorp.com.au, virtualization@...ts.linux-foundation.org, linux-kernel@...r.kernel.org, avi@...hat.com, kvm@...r.kernel.org Subject: Re: [PATCH v3 2/2] virtio-ring: Allocate indirect buffers from cache when possible On Fri, Aug 31, 2012 at 11:36:07AM +0200, Sasha Levin wrote: > On 08/30/2012 03:38 PM, Michael S. Tsirkin wrote: > >> +static unsigned int indirect_alloc_thresh = 16; > > Why 16? Please make is MAX_SG + 1 this makes some sense. > > Wouldn't MAX_SG mean we always allocate from the cache? Isn't the memory waste > too big in this case? Sorry. I really meant MAX_SKB_FRAGS + 1. MAX_SKB_FRAGS is 17 so gets us threshold of 18. It is less than the size of an skb+shinfo itself so - does it look too big to you? Also why do you think 16 is not too big but 18 is? If there's a reason then I am fine with 16 too but then please put it in code comment near where the value is set. Yes this means virtio net always allocates from cache but this is a good thing, isn't it? Gets us more consistent performance. -- MST -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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