Date: Wed, 5 Aug 2020 09:36:52 -0700 (PDT) From: Don Lewis <truckman@FreeBSD.org> To: Mateusz Guzik <mjg@FreeBSD.org> Cc: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: Re: svn commit: r363891 - head/sys/kern Message-ID: <tkrat.62900c56fff65422@FreeBSD.org> In-Reply-To: <202008050924.0759Oc3H010909@repo.freebsd.org> References: <202008050924.0759Oc3H010909@repo.freebsd.org>
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On 5 Aug, Mateusz Guzik wrote: > Author: mjg > Date: Wed Aug 5 09:24:38 2020 > New Revision: 363891 > URL: https://svnweb.freebsd.org/changeset/base/363891 > > Log: > cache: reduce zone alignment to 8 bytes > > It used to be sizeof of the given struct to accomodate for 32 bit mips > doing 64 bit loads, but the same can be achieved with requireing just > 64 bit alignment. > > While here reorder struct namecache so that most commonly used fields > are closer. > > Modified: > head/sys/kern/vfs_cache.c > > Modified: head/sys/kern/vfs_cache.c > ============================================================================== > --- head/sys/kern/vfs_cache.c Wed Aug 5 09:24:00 2020 (r363890) > +++ head/sys/kern/vfs_cache.c Wed Aug 5 09:24:38 2020 (r363891) > @@ -122,9 +122,9 @@ _Static_assert(sizeof(struct negstate) <= sizeof(struc > "the state must fit in a union with a pointer without growing it"); > > struct namecache { > - CK_LIST_ENTRY(namecache) nc_hash;/* hash chain */ > LIST_ENTRY(namecache) nc_src; /* source vnode list */ > TAILQ_ENTRY(namecache) nc_dst; /* destination vnode list */ > + CK_LIST_ENTRY(namecache) nc_hash;/* hash chain */ > struct vnode *nc_dvp; /* vnode of parent of name */ > union { > struct vnode *nu_vp; /* vnode the name refers to */ > @@ -142,6 +142,8 @@ struct namecache { > * to be stored. The nc_dotdottime field is used when a cache entry is mapping > * both a non-dotdot directory name plus dotdot for the directory's > * parent. > + * > + * See below for alignment requirement. > */ > struct namecache_ts { > struct timespec nc_time; /* timespec provided by fs */ > @@ -150,6 +152,14 @@ struct namecache_ts { > struct namecache nc_nc; > }; > > +/* > + * At least mips n32 performs 64-bit accesses to timespec as found > + * in namecache_ts and requires them to be aligned. Since others > + * may be in the same spot suffer a little bit and enforce the > + * alignment for everyone. Note this is a nop for 64-bit platforms. > + */ > +#define CACHE_ZONE_ALIGNMENT UMA_ALIGNOF(time_t) time_t is only 32 bits on i386
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