From mboxrd@z Thu Jan 1 00:00:00 1970 From: Boris Ostrovsky Subject: Re: [PATCH 2/4] xen/events: document behaviour when scanning the start word for events Date: Thu, 15 Aug 2013 10:10:15 -0400 Message-ID: <520CE147.40209@oracle.com> References: <1376569267-11653-1-git-send-email-david.vrabel@citrix.com> <1376569267-11653-3-git-send-email-david.vrabel@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1376569267-11653-3-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 Cc: xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On 08/15/2013 08:21 AM, David Vrabel wrote: > From: David Vrabel > > The original comment on the scanning of the start word on the 2nd pass > did not reflect the actual behaviour (the code was incorrectly masking > bit_idx instead of the pending word itself). > > The documented behaviour is not actually required since if event were > pending in the MSBs, they would be immediately scanned anyway as we go > through the loop again. > > Update the documentation to reflect this (instead of trying to change > the behaviour). > > Signed-off-by: David Vrabel > --- > drivers/xen/events.c | 17 ++++++++++++----- > 1 files changed, 12 insertions(+), 5 deletions(-) > > diff --git a/drivers/xen/events.c b/drivers/xen/events.c > index a58ac43..f866f50 100644 > --- a/drivers/xen/events.c > +++ b/drivers/xen/events.c > @@ -1379,14 +1379,21 @@ static void __xen_evtchn_do_upcall(void) > > pending_bits = active_evtchns(cpu, s, word_idx); > bit_idx = 0; /* usually scan entire word from start */ > + /* > + * We scan the starting word in two parts. > + * > + * 1st time: start in the middle, scanning the > + * MSBs. I think MSB stands for most significant *byte*. 'msb' is for *bit*. Or just say 'upper bits'. Reviewed-by: Boris Ostrovsky > + * > + * 2nd time: scan the whole word (not just the > + * parts skipped in the first pass) -- if an > + * event in the previously scanned bits is > + * pending again it would just be scanned on > + * the next loop anyway. > + */ > if (word_idx == start_word_idx) { > - /* We scan the starting word in two parts */ > if (i == 0) > - /* 1st time: start in the middle */ > bit_idx = start_bit_idx; > - else > - /* 2nd time: mask bits done already */ > - bit_idx &= (1UL << start_bit_idx) - 1; > } > > do {