From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <4CD67825.2080004@domain.hid> Date: Sun, 07 Nov 2010 10:57:57 +0100 From: Gilles Chanteperdrix MIME-Version: 1.0 References: <4CC82C8D.3080808@domain.hid> <4CD1DC1B.8060407@domain.hid> <4CD1DE12.5010309@domain.hid> <4CD1E890.5010702@domain.hid> <4CD1EC2F.4040603@domain.hid> <4CD1ED16.8030103@domain.hid> <4CD1EDA8.10007@domain.hid> <4CD1F33C.5070208@domain.hid> <4CD1F3F5.5080505@domain.hid> <4CD1F4FE.9020908@domain.hid> <4CD1F69B.9070100@domain.hid> <4CD1F906.1070703@domain.hid> <4CD1FABD.1080301@domain.hid> <4CD2612C.2070507@domain.hid> <4CD279F7.7070502@domain.hid> <4CD27C46.8010302@domain.hid> <4CD27DC2.7060607@domain.hid> <4CD2A96B.3080001@domain.hid> <4CD2B2A7.9010900@domain.hid> <4CD2C50F.1090604@domain.hid> <4CD32E76.3080004@domain.hid> <4CD33F0C.1050403@domain.hid> <4CD340AA.60002@domain.hid> <4CD34355.5020304@domain.hid> <4CD35DC7.1000507@domain.hid> <4CD3DAC5.6000400@domain.hid> <4CD4A0EF.1@domain.hid> <4CD5B9FC.6050602@domain.hid> <4CD5BC82.6060106@domain.hid> <1289083796.1842.239.camel@domain.hid> <4CD5FA26.4090504@domain.hid> <4CD663F2.2080704@domain.hid> <4CD6756A.4040806@domain.hid> In-Reply-To: <4CD6756A.4040806@domain.hid> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Subject: Re: [Xenomai-core] Potential problem with rt_eepro100 List-Id: Xenomai life and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Jan Kiszka Cc: "xenomai@xenomai.org" Jan Kiszka wrote: > Am 07.11.2010 09:31, Gilles Chanteperdrix wrote: >> Jan Kiszka wrote: >>>>> Anyway, after some thoughts, I think we are going to try and make the >>>>> current situation work instead of going back to the old way. >>>>> >>>>> You can find the patch which attempts to do so here: >>>>> http://sisyphus.hd.free.fr/~gilles/sched_status.txt >>>> Ack. At last, this addresses the real issues without asking for >>>> regression funkiness: fix the lack of barrier before testing XNSCHED in >>> Check the kernel, we actually need it on both sides. Wherever the final >>> barriers will be, we should leave a comment behind why they are there. >>> Could be picked up from kernel/smp.c. >> We have it on both sides: the non-local flags are modified while holding >> the nklock. Unlocking the nklock implies a barrier. > > I think this does not work if nklock is used nested, ie. hold across > xnsched_set_resched and the next xnpod_schedule. Ok. There is a race here, even without nesting, we need a barrier before sending the IPI. >>> I do not understand the split logic - or some bits are simply not yet >>> migrated. XNHDEFER, XNSWLOCK, XNKCOUT are all local-only as well, no? >>> Then better put them in the _local_ status field, that's more consistent >>> (and would help if we once wanted to optimize their cache line usage). >> Maybe the naming is not good the. ->status is everything which is >> modified under nklock, ->lstatus is for XNINIRQ and XNHTICK which are >> modified without holding the nklock. > > And this is not a good clustering IMHO as it makes no difference for a > local-only flag if it is protected by nklock or not (as long as IRQs are > off, of course). What makes a difference it the CPU using the related > field. If we group according to local and remote usage, less cache line > bouncing can be achieved (of both fields are also cache line aligned, > but that is a second step that only helps if the first is made). The two status are in the same cache line. -- Gilles.