linux-kernel - Re: [PATCH v4 09/10] swiotlb-xen: support autotranslate guests

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <20130830132312.GF21239@phenom.dumpdata.com>
Date:	Fri, 30 Aug 2013 09:23:12 -0400
From:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
To:	Stefano Stabellini <stefano.stabellini@...citrix.com>
Cc:	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, Ian.Campbell@...rix.com
Subject: Re: [PATCH v4 09/10] swiotlb-xen: support autotranslate guests

> > Did you run any performance tests to see if adding the extra
> > spinlock (as the native SWIOTLB already has its own lock) and handling
> > of the tree is affecting it?

.. bla bla..

> I haven't done any measurements but consider that the spin_lock is
> already only used to access the red-black tree that keeps track of
> dma_addr -> phys_addr mappings.
> So it's taken at setup time once, then every time we call
> xen_bus_to_phys and the guest is an autotraslate guest.
> If the guest is not autotraslate there are no additional locks.
> 
> That makes me realize that we don't need any spin_locks at all: there
> are no risks of concurrent accesses and modifications of the tree
> because there are no changes on the tree once it's setup at boot time.
> We can get rid of the spin_lock entirely as concurrent read accesses on
> the tree are obviously fine.

Nice :-) I think that (and the goto) were the only concerns I had.

Thanks!
--
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/