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Registered in England and Wales under Company Registration No. 3798903 From: David Howells In-Reply-To: References: <8722207799c342e780e1162a983dc48b@AcuMS.aculab.com> <855.1692047347@warthog.procyon.org.uk> <5247.1692049208@warthog.procyon.org.uk> <440141.1692179410@warthog.procyon.org.uk> To: David Laight Cc: dhowells@redhat.com, Linus Torvalds , Alexander Viro , Jens Axboe , Christoph Hellwig , Christian Brauner , Matthew Wilcox , "jlayton@kernel.org" , "linux-block@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" , "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" Subject: Re: [RFC PATCH v2] iov_iter: Convert iterate*() to inline funcs MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <532384.1692184743.1@warthog.procyon.org.uk> Date: Wed, 16 Aug 2023 12:19:03 +0100 Message-ID: <532385.1692184743@warthog.procyon.org.uk> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.3 X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 981BF80027 X-Stat-Signature: 9gjrxeyiti9tfwebqnbkwtw1yzg3erg8 X-Rspam-User: X-HE-Tag: 1692184751-205142 X-HE-Meta: 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 FI1DZX63 6dfse8+Lnd8c+EHtNDyZoTX1Elyl8vFKVe/yG7oiQQHrumqikOLELbeLKUvAU9r8w/wjoKMRxZP6fLGT++MS/1wAz+kWcPZXQ0YRSuFOf12jagUF8TsBDNlnauEKiFFH56pgjx3BRcjeNOMbRFfJL4aQ+ZIJcKTH1lP4ZJRwJ24g1BzuqlpbrQrWOtuW2MlxfDJ7ufgYSd+0RD+2vDNss1nBQANByPujjP5o7qXyJSSN7GZVhi+zp9UsHCI5UesGX02bUgjoxQnzxlsd5Z5G5D0rT9CZ+D/N/S7fHC1QfPOM4Q+Mg3ne9luI97hteQyH9aWsWl59RjHYo5KbKsvGZ0ZoskgwFvLpqo/Ed X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: David Laight wrote: > > That can't be avoided if I convert everything to inline functions and > > function pointers - but the optimiser can get rid of it where it can > > inline the step function. > > AFAICT the IOVEC one was only called directly. I've made some changes that I'll post shortly, and I now get this: ... <+36>: cmpb $0x0,0x1(%rdx) # iter->copy_mc ... <+46>: je 0xffffffff81779aae <_copy_from_iter+98> <+48>: jmp 0xffffffff81779a87 <_copy_from_iter+59> ... # Handle ->copy_mc == true <+59>: mov 0x38(%rsp),%rax <+64>: sub %gs:0x28,%rax <+73>: jne 0xffffffff81779db1 <_copy_from_iter+869> <+79>: add $0x40,%rsp <+83>: pop %rbx <+84>: pop %rbp <+85>: pop %r12 <+87>: pop %r13 <+89>: pop %r14 <+91>: pop %r15 <+93>: jmp 0xffffffff81777934 <__copy_from_iter_mc> ... # ITER_UBUF <+121>: mov (%rdx),%al <+123>: cmp $0x5,%al <+125>: jne 0xffffffff81779b01 <_copy_from_iter+181> ... <+147>: call 0xffffffff817777ee <__access_ok> <+152>: test %al,%al <+154>: je 0xffffffff81779af9 <_copy_from_iter+173> <+156>: nop <+157>: nop <+158>: nop <+159>: mov %r12,%rdi <+162>: mov %rdx,%rsi <+165>: rep movsb %ds:(%rsi),%es:(%rdi) ... # ITER_IOVEC <+181>: test %al,%al <+183>: jne 0xffffffff81779b8d <_copy_from_iter+321> ... <+234>: call 0xffffffff817777ee <__access_ok> <+239>: test %al,%al <+241>: je 0xffffffff81779b54 <_copy_from_iter+264> <+243>: nop <+244>: nop <+245>: nop <+246>: lea (%r12,%r15,1),%rax <+250>: mov %r8,%rsi <+253>: mov %rax,%rdi <+256>: rep movsb %ds:(%rsi),%es:(%rdi) ... # ITER_BVEC <+321>: cmp $0x2,%al <+323>: jne 0xffffffff81779c1f <_copy_from_iter+467> ... <+375>: call 0xffffffff81777282 ... <+431>: rep movsb %ds:(%rsi),%es:(%rdi) ... # ITER_KVEC <+467>: cmp $0x1,%al <+469>: jne 0xffffffff81779c82 <_copy_from_iter+566> ... <+526>: rep movsb %ds:(%rsi),%es:(%rdi) ... # ITER_XARRAY <+566>: cmp $0x3,%al <+568>: jne 0xffffffff81779d9d <_copy_from_iter+849> ... <+639>: call 0xffffffff81126bcf <__rcu_read_lock> ... <+651>: call 0xffffffff81d5ed97 ... <+764>: call 0xffffffff817772a7 ... <+806>: rep movsb %ds:(%rsi),%es:(%rdi) ... # ITER_DISCARD/default <+849>: sub %rbx,0x18(%rbp) <+853>: mov 0x38(%rsp),%rax <+858>: sub %gs:0x28,%rax <+867>: je 0xffffffff81779db6 <_copy_from_iter+874> <+869>: call 0xffffffff81d6578c <__stack_chk_fail> <+874>: add $0x40,%rsp <+878>: mov %rbx,%rax <+881>: pop %rbx <+882>: pop %rbp <+883>: pop %r12 <+885>: pop %r13 <+887>: pop %r14 <+889>: pop %r15 <+891>: jmp 0xffffffff81d72920 <__x86_return_thunk> David