From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCHv1] xen/evtchn: dynamically grow pending event channel ring Date: Thu, 26 Nov 2015 18:49:13 +0000 Message-ID: <56575429.5000601@citrix.com> References: <1448554475-25754-1-git-send-email-david.vrabel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1a21ba-0000sM-3i for xen-devel@lists.xenproject.org; Thu, 26 Nov 2015 18:49:18 +0000 In-Reply-To: <1448554475-25754-1-git-send-email-david.vrabel@citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: David Vrabel , xen-devel@lists.xenproject.org Cc: Boris Ostrovsky List-Id: xen-devel@lists.xenproject.org On 26/11/15 16:14, David Vrabel wrote: > If more than 1024 event channels are bound to a evtchn device then it > possible (even with well behaved applications) for the ring to > overflow and events to be lost (reported as an -EFBIG error). > > Dynamically increase the size of the ring so there is always enough > space for all bound events. Well behaved applicables that only unmask > events after draining them from the ring can thus no longer lose > events. > > However, an application could unmask an event before draining it, > allowing multiple entries per port to accumulate in the ring, and a > overflow could still occur. So the overflow detection and reporting > is retained. > > The ring size is initially only 64 entries so the common use case of > an application only binding a few events will use less memory than > before. The ring size may grow to 512 KiB (enough for all 2^17 > possible channels). This order 7 kmalloc() may fail due to memory > fragmentation, so we fall back to trying vmalloc(). > > Signed-off-by: David Vrabel Reviewed-by: Andrew Cooper