Date: Fri, 14 Feb 2014 02:07:51 +0000 From: "Gumpula, Suresh" <Suresh.Gumpula@netapp.com> To: John-Mark Gurney <jmg@funkthat.com> Cc: "freebsd-hackers@freebsd.org" <freebsd-hackers@freebsd.org>, Ian Lepore <ian@freebsd.org> Subject: RE: malloc(9) and its alignment Message-ID: <D29CB80EBA4DEA4D91181928AAF51538438F10CC@SACEXCMBX04-PRD.hq.netapp.com> In-Reply-To: <20140212220705.GV34851@funkthat.com> References: <D29CB80EBA4DEA4D91181928AAF51538438EED0A@SACEXCMBX04-PRD.hq.netapp.com> <1392214788.1145.52.camel@revolution.hippie.lan> <D29CB80EBA4DEA4D91181928AAF51538438EF8DC@SACEXCMBX04-PRD.hq.netapp.com> <20140212220705.GV34851@funkthat.com>
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Thanks for the explanation John. How about porting ARM way of handling req=
uired alignment with creation of separate zones
And allocating with uma_zalloc(zone) for AMD64 too for bus_dmamem_alloc?
Thanks
Suresh
-----Original Message-----
From: John-Mark Gurney [mailto:jmg@funkthat.com]=20
Sent: Wednesday, February 12, 2014 5:07 PM
To: Gumpula, Suresh
Cc: Ian Lepore; freebsd-hackers@freebsd.org
Subject: Re: malloc(9) and its alignment
Gumpula, Suresh wrote this message on Wed, Feb 12, 2014 at 19:40 +0000:
> Thanks Ian for the reply. I will look at the ARM code, but I was think=
ing why malloc(9) does not return bucket size aligned pointers.=20
Always returning bucket sizes aligned pointers may not be ideal for a cache=
.. say you have a buffer of 512 bytes, where often only the first
128 bytes are used (but all 512 bytes may be)... If you always align at 51=
2, some cache lines will be more heavily used than others, reducing the eff=
ective size of the cache...
This is only one reason not aligning to size may be better...
--=20
John-Mark Gurney Voice: +1 415 225 5579
"All that I will do, has been done, All that I have, has not."
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