Date: Wed, 31 Dec 2008 12:19:13 +0100 From: Grzegorz Bernacki <gjb@semihalf.com> To: Marcel Moolenaar <xcllnt@mac.com> Cc: arm@freebsd.org, embedded@freebsd.org Subject: Re: Multiple virtual mappings considered harmful on ARM Message-ID: <495B5531.8040604@semihalf.com> In-Reply-To: <D7878EEF-511A-43EF-AE2B-9465C9301674@mac.com> References: <494BAA90.7000801@semihalf.com> <D7878EEF-511A-43EF-AE2B-9465C9301674@mac.com>
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Marcel Moolenaar wrote: > > On Dec 19, 2008, at 6:07 AM, Grzegorz Bernacki wrote: > >> 2. Root cause. >> The root cause of the problem is additional virtual mapping of read/write >> buffers at cluster read/write (sys/kern/vfs_cluster.c, cluster_rbuild(), >> cluster_wbuild(). Buffers for sequential read/write operation are >> concatenated >> and sent to device as one big buffer. Concatenation of buffers uses >> pmap_qenter(), which puts *additional* mapping in the KVA for physical >> area >> already mapped. For each buffer we extract pages it contains and then >> all the >> pages from all the buffers are mapped into new virtual address of new >> buffer. >> So we end up with at least two virtual addresses for each page. > > Could this also affect I-cache coherency by virtue of not > flushing the D-cache properly before synchronizing the > I-cache, as you mention reading? > I am not sure. I can't think of scenario which might lead to I-cache incoherency. Have you experienced any issues with I-cache which might be related described problem? pozdrawiam, Grzesiek
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