From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (qmail 17596 invoked by alias); 29 Apr 2016 13:48:25 -0000 Mailing-List: contact libc-alpha-help@sourceware.org; run by ezmlm Precedence: bulk List-Id: List-Subscribe: List-Archive: List-Post: List-Help: , Sender: libc-alpha-owner@sourceware.org Received: (qmail 17480 invoked by uid 89); 29 Apr 2016 13:48:17 -0000 Authentication-Results: sourceware.org; auth=none X-Virus-Found: No X-Spam-SWARE-Status: No, score=-1.9 required=5.0 tests=BAYES_00,KAM_LAZY_DOMAIN_SECURITY,RP_MATCHES_RCVD autolearn=ham version=3.3.2 spammy=Gabriel, 20042016, stw, cmpldi X-HELO: e24smtp02.br.ibm.com X-IBM-Helo: d24dlp01.br.ibm.com X-IBM-MailFrom: gftg@linux.vnet.ibm.com X-IBM-RcptTo: libc-alpha@sourceware.org Date: Fri, 29 Apr 2016 13:48:00 -0000 From: "Gabriel F. T. Gomes" To: Adhemerval Zanella Cc: libc-alpha@sourceware.org Subject: Re: [PATCH 1/2] powerpc: Zero pad using memset in strncpy/stpncpy Message-ID: <20160429104757.4bdfead2@keller> In-Reply-To: <571F7850.7050605@linaro.org> References: <1461185716-7332-1-git-send-email-gftg@linux.vnet.ibm.com> <5717F3D1.5090003@linaro.org> <20160426104120.535e2f92@keller> <571F7850.7050605@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16042913-0021-0000-0000-00001D77290E X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused X-SW-Source: 2016-04/txt/msg00754.txt.bz2 Thank you for reviewing, Adhemerval. Pushed as 72c11b353ede72931cc474c9071d143d9a05c0d7. On Tue, 26 Apr 2016 11:16:48 -0300 Adhemerval Zanella wrote: > On 26/04/2016 10:41, Gabriel F. T. Gomes wrote: > > On Wed, 20 Apr 2016 18:25:37 -0300 > > Adhemerval Zanella wrote: > > > >> I am ok with this patch, the only nit is it now calls memset for all > >> padding size, where for small padding (less than 16 or maybe 32) I think it would > >> be still faster than calling memset (since dcbtst will be used only for > >> large inputs). However I still not sure if embedding the memset write_LT_32 > >> would yield much gain as well. > > > > Hi, Adhemerval. Thanks for your review. > > > > I also expected that for small amounts of padding, calling memset would > > harm performance. However, I ran some tests, where memset was only > > called for padding amounts greater than 32 bytes, and I didn't notice > > any significant changes in performance. That's the reason why I sent > > this version of the patch, which always calls memset. > > > > I also noticed that bench-strncpy exposes a load-hit-store problem, > > which might be suppressing the difference for small paddings. I have > > plans to fix this in the future, and, if necessary, limit memset to > > greater paddings. > > > > However, right now, I don't see a benefit in adding the check. > > > > > > Fair enough then. > > >> On 20-04-2016 17:55, Gabriel F. T. Gomes wrote: > >>> Call __memset_power8 to pad, with zeros, the remaining bytes in the > >>> dest string on __strncpy_power8 and __stpncpy_power8. This improves > >>> performance when n is larger than the input string, giving ~30% gain for > >>> larger strings without impacting much shorter strings. > >>> > >>> 2016-04-18 Gabriel F. T. Gomes > >>> > >>> * sysdeps/powerpc/powerpc64/power8/strncpy.S: Call memset to pad the > >>> remaining bytes in the dest string, with zeros. > >>> --- > >>> sysdeps/powerpc/powerpc64/power8/strncpy.S | 123 +++++++++++++---------------- > >>> 1 file changed, 56 insertions(+), 67 deletions(-) > >>> > >>> diff --git a/sysdeps/powerpc/powerpc64/power8/strncpy.S b/sysdeps/powerpc/powerpc64/power8/strncpy.S > >>> index 17c3afb..0bb3bd4 100644 > >>> --- a/sysdeps/powerpc/powerpc64/power8/strncpy.S > >>> +++ b/sysdeps/powerpc/powerpc64/power8/strncpy.S > >>> @@ -24,6 +24,8 @@ > >>> # define FUNC_NAME strncpy > >>> #endif > >>> > >>> +#define FRAMESIZE (FRAME_MIN_SIZE+48) > >>> + > >>> /* Implements the function > >>> > >>> char * [r3] strncpy (char *dest [r3], const char *src [r4], size_t n [r5]) > >>> @@ -54,8 +56,7 @@ EALIGN (FUNC_NAME, 4, 0) > >>> addi r10,r4,16 > >>> rlwinm r9,r4,0,19,19 > >>> > >>> - /* Since it is a leaf function, save some non-volatile registers on the > >>> - protected/red zone. */ > >>> + /* Save some non-volatile registers on the stack. */ > >>> std r26,-48(r1) > >>> std r27,-40(r1) > >>> > >>> @@ -69,6 +70,14 @@ EALIGN (FUNC_NAME, 4, 0) > >>> std r30,-16(r1) > >>> std r31,-8(r1) > >>> > >>> + /* Update CFI. */ > >>> + cfi_offset(r26, -48) > >>> + cfi_offset(r27, -40) > >>> + cfi_offset(r28, -32) > >>> + cfi_offset(r29, -24) > >>> + cfi_offset(r30, -16) > >>> + cfi_offset(r31, -8) > >>> + > >>> beq cr7,L(unaligned_lt_16) > >>> rldicl r9,r4,0,61 > >>> subfic r8,r9,8 > >>> @@ -180,74 +189,58 @@ L(short_path_loop_end): > >>> ld r31,-8(r1) > >>> blr > >>> > >>> - /* This code pads the remainder dest with NULL bytes. The algorithm > >>> - calculate the remanining size and issues a doubleword unrolled > >>> - loops followed by a byte a byte set. */ > >>> + /* This code pads the remainder of dest with NULL bytes. The algorithm > >>> + calculates the remaining size and calls memset. */ > >>> .align 4 > >>> L(zero_pad_start): > >>> mr r5,r10 > >>> mr r9,r6 > >>> L(zero_pad_start_1): > >>> - srdi. r8,r5,r3 > >>> - mr r10,r9 > >>> -#ifdef USE_AS_STPNCPY > >>> - mr r3,r9 > >>> + /* At this point: > >>> + - r5 holds the number of bytes that still have to be written to > >>> + dest. > >>> + - r9 points to the position, in dest, where the first null byte > >>> + will be written. > >>> + The above statements are true both when control reaches this label > >>> + from a branch or when falling through the previous lines. */ > >>> +#ifndef USE_AS_STPNCPY > >>> + mr r30,r3 /* Save the return value of strncpy. */ > >>> +#endif > >>> + /* Prepare the call to memset. */ > >>> + mr r3,r9 /* Pointer to the area to be zero-filled. */ > >>> + li r4,0 /* Byte to be written (zero). */ > >>> + > >>> + /* We delayed the creation of the stack frame, as well as the saving of > >>> + the link register, because only at this point, we are sure that > >>> + doing so is actually needed. */ > >>> + > >>> + /* Save the link register. */ > >>> + mflr r0 > >>> + std r0,16(r1) > >>> + cfi_offset(lr, 16) > >>> + > >>> + /* Create the stack frame. */ > >>> + stdu r1,-FRAMESIZE(r1) > >>> + cfi_adjust_cfa_offset(FRAMESIZE) > >>> + > >>> + bl __memset_power8 > >>> + nop > >>> + > >>> + /* Restore the stack frame. */ > >>> + addi r1,r1,FRAMESIZE > >>> + cfi_adjust_cfa_offset(-FRAMESIZE) > >>> + /* Restore the link register. */ > >>> + ld r0,16(r1) > >>> + mtlr r0 > >>> + > >>> +#ifndef USE_AS_STPNCPY > >>> + mr r3,r30 /* Restore the return value of strncpy, i.e.: > >>> + dest. For stpncpy, the return value is the > >>> + same as return value of memset. */ > >>> #endif > >>> - beq- cr0,L(zero_pad_loop_b_start) > >>> - cmpldi cr7,r8,1 > >>> - li cr7,0 > >>> - std r7,0(r9) > >>> - beq cr7,L(zero_pad_loop_b_prepare) > >>> - addic. r8,r8,-2 > >>> - addi r10,r9,r16 > >>> - std r7,8(r9) > >>> - beq cr0,L(zero_pad_loop_dw_2) > >>> - std r7,16(r9) > >>> - li r9,0 > >>> - b L(zero_pad_loop_dw_1) > >>> - > >>> - .align 4 > >>> -L(zero_pad_loop_dw): > >>> - addi r10,r10,16 > >>> - std r9,-8(r10) > >>> - beq cr0,L(zero_pad_loop_dw_2) > >>> - std r9,0(r10) > >>> -L(zero_pad_loop_dw_1): > >>> - cmpldi cr7,r8,1 > >>> - std r9,0(r10) > >>> - addic. r8,r8,-2 > >>> - bne cr7,L(zero_pad_loop_dw) > >>> - addi r10,r10,8 > >>> -L(zero_pad_loop_dw_2): > >>> - rldicl r5,r5,0,61 > >>> -L(zero_pad_loop_b_start): > >>> - cmpdi cr7,r5,0 > >>> - addi r5,r5,-1 > >>> - addi r9,r10,-1 > >>> - add r10,r10,5 > >>> - subf r10,r9,r10 > >>> - li r8,0 > >>> - beq- cr7,L(short_path_loop_end) > >>> - > >>> - /* Write remaining 1-8 bytes. */ > >>> - .align 4 > >>> - addi r9,r9,1 > >>> - mtocrf 0x1,r10 > >>> - bf 29,4f > >>> - stw r8,0(r9) > >>> - addi r9,r9,4 > >>> - > >>> - .align 4 > >>> -4: bf 30,2f > >>> - sth r8,0(r9) > >>> - addi r9,r9,2 > >>> - > >>> - .align 4 > >>> -2: bf 31,1f > >>> - stb r8,0(r9) > >>> > >>> - /* Restore non-volatile registers. */ > >>> -1: ld r26,-48(r1) > >>> + /* Restore non-volatile registers and return. */ > >>> + ld r26,-48(r1) > >>> ld r27,-40(r1) > >>> ld r28,-32(r1) > >>> ld r29,-24(r1) > >>> @@ -443,10 +436,6 @@ L(short_path_prepare_2_3): > >>> mr r4,r28 > >>> mr r9,r29 > >>> b L(short_path_2) > >>> -L(zero_pad_loop_b_prepare): > >>> - addi r10,r9,8 > >>> - rldicl r5,r5,0,61 > >>> - b L(zero_pad_loop_b_start) > >>> L(zero_pad_start_prepare_1): > >>> mr r5,r6 > >>> mr r9,r8 > >>> > >> > > >