Date: Tue, 4 Nov 2014 12:40:41 +0100 From: Mateusz Guzik <mjguzik@gmail.com> To: Hans Petter Selasky <hselasky@FreeBSD.org> Cc: svn-src-head@freebsd.org, svn-src-all@freebsd.org, src-committers@freebsd.org Subject: Re: svn commit: r274088 - head/sys/kern Message-ID: <20141104114041.GA21297@dft-labs.eu> In-Reply-To: <201411041129.sA4BTnwX030600@svn.freebsd.org> References: <201411041129.sA4BTnwX030600@svn.freebsd.org>
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On Tue, Nov 04, 2014 at 11:29:49AM +0000, Hans Petter Selasky wrote: > Author: hselasky > Date: Tue Nov 4 11:29:49 2014 > New Revision: 274088 > URL: https://svnweb.freebsd.org/changeset/base/274088 > > Log: > Simplify logic a bit. Ensure data buffer is properly aligned, > especially for platforms where unaligned access is not allowed. Make > it possible to override the small buffer size. > > A simple continuous read string test using libusb showed a reduction > in CPU usage from roughly 10% to less than 1% using a dual-core GHz > CPU, when the malloc() operation was skipped for small buffers. > > MFC after: 2 weeks > > Modified: > head/sys/kern/sys_generic.c > > Modified: head/sys/kern/sys_generic.c > ============================================================================== > --- head/sys/kern/sys_generic.c Tue Nov 4 10:25:52 2014 (r274087) > +++ head/sys/kern/sys_generic.c Tue Nov 4 11:29:49 2014 (r274088) > @@ -646,10 +646,13 @@ struct ioctl_args { > int > sys_ioctl(struct thread *td, struct ioctl_args *uap) > { > +#ifndef SYS_IOCTL_SMALL_SIZE > +#define SYS_IOCTL_SMALL_SIZE 128 > +#endif > + u_char smalldata[SYS_IOCTL_SMALL_SIZE] __aligned(8); Should not you align to word size instead? Also maybe it would be beneficial to derive the limit from KSTACK_PAGES (something silly like KSTACK_PAGES * 32 or something), which I believe would address earlier complaints. > u_long com; > int arg, error; > u_int size; > - u_char smalldata[128]; > caddr_t data; > > if (uap->com > 0xffffffff) { > @@ -682,10 +685,10 @@ sys_ioctl(struct thread *td, struct ioct > data = (void *)&arg; > size = 0; > } else { > - if (size <= sizeof(smalldata)) > - data = smalldata; > - else > + if (size > SYS_IOCTL_SMALL_SIZE) > data = malloc((u_long)size, M_IOCTLOPS, M_WAITOK); > + else > + data = smalldata; > } > } else > data = (void *)&uap->data; > @@ -707,7 +710,7 @@ sys_ioctl(struct thread *td, struct ioct > error = copyout(data, uap->data, (u_int)size); > > out: > - if (size > 0 && data != (caddr_t)&smalldata) > + if (size > SYS_IOCTL_SMALL_SIZE) > free(data, M_IOCTLOPS); > return (error); > } > -- Mateusz Guzik <mjguzik gmail.com>
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