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path: root/arch/powerpc/lib/copyuser_power7.S
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2015-03-16powerpc: Change vrX register defines to vX to match gcc and glibcAnton Blanchard
As our various loops (copy, string, crypto etc) get more complicated, we want to share implementations between userspace (eg glibc) and the kernel. We also want to write userspace test harnesses to put in tools/testing/selftest. One gratuitous difference between userspace and the kernel is the VMX register definitions - the kernel uses vrX whereas both gcc and glibc use vX. Change the kernel to match userspace. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2014-10-29powerpc: Fix comment typos 'CONFiG_ALTIVEC'Paul Bolle
Signed-off-by: Paul Bolle <pebolle@tiscali.nl> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2014-04-23powerpc: Fix unsafe accesses to parameter area in ELFv2Ulrich Weigand
Some of the assembler files in lib/ make use of the fact that in the ELFv1 ABI, the caller guarantees to provide stack space to save the parameter registers r3 ... r10. This guarantee is no longer present in ELFv2 for functions that have no variable argument list and no more than 8 arguments. Change the affected routines to temporarily store registers in the red zone and/or the top of their own stack frame (in the space provided to save r31 .. r29, which is actually not used in these routines). In opal_query_takeover, simply always allocate a stack frame; the routine is not performance critical. Signed-off-by: Ulrich Weigand <ulrich.weigand@de.ibm.com> Signed-off-by: Anton Blanchard <anton@samba.org>
2014-04-23powerpc: Fix ABIv2 issues with stack offsets in assembly codeAnton Blanchard
Fix STK_PARAM and use it instead of hardcoding ABIv1 offsets. Signed-off-by: Anton Blanchard <anton@samba.org>
2014-04-23powerpc: No need to use dot symbols when branching to a functionAnton Blanchard
binutils is smart enough to know that a branch to a function descriptor is actually a branch to the functions text address. Alan tells me that binutils has been doing this for 9 years. Signed-off-by: Anton Blanchard <anton@samba.org>
2013-10-11powerpc: Fix endian issues in VMX copy loopsAnton Blanchard
Fix the permute loops for little endian. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2013-05-31powerpc/pseries: Improve stream generation comments in copypage/userMichael Neuling
No code changes, just documenting what's happening a little better. Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-08-24powerpc: Fix VMX in interrupt check in POWER7 copy loopsAnton Blanchard
The enhanced prefetch hint patches corrupt the condition register that was used to check if we are in interrupt. Fix this by using cr1. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-08-24powerpc: POWER7 copy_to_user/copy_from_user patch applied twiceAnton Blanchard
"powerpc: Use enhanced touch instructions in POWER7 copy_to_user/copy_from_user" was applied twice. Remove one. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-07-10powerpc: Merge STK_REG/PARAM/FRAMESIZEMichael Neuling
Merge the defines of STACKFRAMESIZE, STK_REG, STK_PARAM from different places. Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-07-10powerpc: Fix usage of register macros getting ready for %r0 changeMichael Neuling
Anything that uses a constructed instruction (ie. from ppc-opcode.h), need to use the new R0 macro, as %r0 is not going to work. Also convert usages of macros where we are just determining an offset (usually for a load/store), like: std r14,STK_REG(r14)(r1) Can't use STK_REG(r14) as %r14 doesn't work in the STK_REG macro since it's just calculating an offset. Signed-off-by: Michael Neuling <mikey@neuling.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-07-03powerpc: Use enhanced touch instructions in POWER7 copy_to_user/copy_from_userAnton Blanchard
Version 2.06 of the POWER ISA introduced enhanced touch instructions, allowing us to specify a number of attributes including the length of a stream. This patch adds a software stream for both loads and stores in the POWER7 copy_tofrom_user loop. Since the setup is quite complicated and we have to use an eieio to ensure correct ordering of the "GO" command we only do this for copies above 4kB. To quantify any performance improvements we need a working set bigger than the caches so we operate on a 1GB file: # dd if=/dev/zero of=/tmp/foo bs=1M count=1024 And we compare how fast we can read the file: # dd if=/tmp/foo of=/dev/null bs=1M before: 7.7 GB/s after: 9.6 GB/s A 25% improvement. The worst case for this patch will be a completely L1 cache contained copy of just over 4kB. We can test this with the copy_to_user testcase we used to tune copy_tofrom_user originally: http://ozlabs.org/~anton/junkcode/copy_to_user.c # time ./copy_to_user2 -l 4224 -i 10000000 before: 6.807 s after: 6.946 s A 2% slowdown, which seems reasonable considering our data is unlikely to be completely L1 contained. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-07-03powerpc: Rename copyuser_power7_vmx.c to vmx-helper.cAnton Blanchard
Subsequent patches will add more VMX library functions and it makes sense to keep all the c-code helper functions in the one file. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2012-07-03powerpc: Use enhanced touch instructions in POWER7 copy_to_user/copy_from_userAnton Blanchard
Version 2.06 of the POWER ISA introduced enhanced touch instructions, allowing us to specify a number of attributes including the length of a stream. This patch adds a software stream for both loads and stores in the POWER7 copy_tofrom_user loop. Since the setup is quite complicated and we have to use an eieio to ensure correct ordering of the "GO" command we only do this for copies above 4kB. To quantify any performance improvements we need a working set bigger than the caches so we operate on a 1GB file: # dd if=/dev/zero of=/tmp/foo bs=1M count=1024 And we compare how fast we can read the file: # dd if=/tmp/foo of=/dev/null bs=1M before: 7.7 GB/s after: 9.6 GB/s A 25% improvement. The worst case for this patch will be a completely L1 cache contained copy of just over 4kB. We can test this with the copy_to_user testcase we used to tune copy_tofrom_user originally: http://ozlabs.org/~anton/junkcode/copy_to_user.c # time ./copy_to_user2 -l 4224 -i 10000000 before: 6.807 s after: 6.946 s A 2% slowdown, which seems reasonable considering our data is unlikely to be completely L1 contained. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
2011-12-19powerpc: POWER7 optimised copy_to_user/copy_from_user using VMXAnton Blanchard
Implement a POWER7 optimised copy_to_user/copy_from_user using VMX. For large aligned copies this new loop is over 10% faster, and for large unaligned copies it is over 200% faster. If we take a fault we fall back to the old version, this keeps things relatively simple and easy to verify. On POWER7 unaligned stores rarely slow down - they only flush when a store crosses a 4KB page boundary. Furthermore this flush is handled completely in hardware and should be 20-30 cycles. Unaligned loads on the other hand flush much more often - whenever crossing a 128 byte cache line, or a 32 byte sector if either sector is an L1 miss. Considering this information we really want to get the loads aligned and not worry about the alignment of the stores. Microbenchmarks confirm that this approach is much faster than the current unaligned copy loop that uses shifts and rotates to ensure both loads and stores are aligned. We also want to try and do the stores in cacheline aligned, cacheline sized chunks. If the store queue is unable to merge an entire cacheline of stores then the L2 cache will have to do a read/modify/write. Even worse, we will serialise this with the stores in the next iteration of the copy loop since both iterations hit the same cacheline. Based on this, the new loop does the following things: 1 - 127 bytes Get the source 8 byte aligned and use 8 byte loads and stores. Pretty boring and similar to how the current loop works. 128 - 4095 bytes Get the source 8 byte aligned and use 8 byte loads and stores, 1 cacheline at a time. We aren't doing the stores in cacheline aligned chunks so we will potentially serialise once per cacheline. Even so it is much better than the loop we have today. 4096 - bytes If both source and destination have the same alignment get them both 16 byte aligned, then get the destination cacheline aligned. Do cacheline sized loads and stores using VMX. If source and destination do not have the same alignment, we get the destination cacheline aligned, and use permute to do aligned loads. In both cases the VMX loop should be optimal - we always do aligned loads and stores and are always doing stores in cacheline aligned, cacheline sized chunks. To be able to use VMX we must be careful about interrupts and sleeping. We don't use the VMX loop when in an interrupt (which should be rare anyway) and we wrap the VMX loop in disable/enable_pagefault and fall back to the existing copy_tofrom_user loop if we do need to sleep. The VMX breakpoint of 4096 bytes was chosen using this microbenchmark: http://ozlabs.org/~anton/junkcode/copy_to_user.c Since we are using VMX and there is a cost to saving and restoring the user VMX state there are two broad cases we need to benchmark: - Best case - userspace never uses VMX - Worst case - userspace always uses VMX In reality a userspace process will sit somewhere between these two extremes. Since we need to test both aligned and unaligned copies we end up with 4 combinations. The point at which the VMX loop begins to win is: 0% VMX aligned 2048 bytes unaligned 2048 bytes 100% VMX aligned 16384 bytes unaligned 8192 bytes Considering this is a microbenchmark, the data is hot in cache and the VMX loop has better store queue merging properties we set the breakpoint to 4096 bytes, a little below the unaligned breakpoints. Some future optimisations we can look at: - Looking at the perf data, a significant part of the cost when a task is always using VMX is the extra exception we take to restore the VMX state. As such we should do something similar to the x86 optimisation that restores FPU state for heavy users. ie: /* * If the task has used fpu the last 5 timeslices, just do a full * restore of the math state immediately to avoid the trap; the * chances of needing FPU soon are obviously high now */ preload_fpu = tsk_used_math(next_p) && next_p->fpu_counter > 5; and /* * fpu_counter contains the number of consecutive context switches * that the FPU is used. If this is over a threshold, the lazy fpu * saving becomes unlazy to save the trap. This is an unsigned char * so that after 256 times the counter wraps and the behavior turns * lazy again; this to deal with bursty apps that only use FPU for * a short time */ - We could create a paca bit to mirror the VMX enabled MSR bit and check that first, avoiding multiple calls to calling enable_kernel_altivec. That should help with iovec based system calls like readv. - We could have two VMX breakpoints, one for when we know the user VMX state is loaded into the registers and one when it isn't. This could be a second bit in the paca so we can calculate the break points quickly. - One suggestion from Ben was to save and restore the VSX registers we use inline instead of using enable_kernel_altivec. [BenH: Fixed a problem with preempt and fixed build without CONFIG_ALTIVEC] Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>