Date: Wed, 18 Nov 2020 19:47:24 +0000 (UTC) From: Mateusz Guzik <mjg@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r367814 - head/sys/sys Message-ID: <202011181947.0AIJlOXu003910@repo.freebsd.org>
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Author: mjg Date: Wed Nov 18 19:47:24 2020 New Revision: 367814 URL: https://svnweb.freebsd.org/changeset/base/367814 Log: fd: reorder struct file to reduce false sharing The size on LP64 is 80 bytes, which is just more than a cacheline, does not lend itself to easy shrinking and rounding up to 2 would be a huge waste given NOFREE marker. The least which can be done is to reorder it so that most commonly used fields are less likely to span different lines, and consequently suffer less false sharing. With the change at hand most commonly used fields land in the same line about 3/4 of the time, as opposed to 2/4. Modified: head/sys/sys/file.h Modified: head/sys/sys/file.h ============================================================================== --- head/sys/sys/file.h Wed Nov 18 19:44:30 2020 (r367813) +++ head/sys/sys/file.h Wed Nov 18 19:47:24 2020 (r367814) @@ -177,14 +177,14 @@ struct fadvise_info { }; struct file { + volatile u_int f_flag; /* see fcntl.h */ + volatile u_int f_count; /* reference count */ void *f_data; /* file descriptor specific data */ struct fileops *f_ops; /* File operations */ - struct ucred *f_cred; /* associated credentials. */ struct vnode *f_vnode; /* NULL or applicable vnode */ + struct ucred *f_cred; /* associated credentials. */ short f_type; /* descriptor type */ short f_vnread_flags; /* (f) Sleep lock for f_offset */ - volatile u_int f_flag; /* see fcntl.h */ - volatile u_int f_count; /* reference count */ /* * DTYPE_VNODE specific fields. */
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