From: Petr Tesarik <ptesarik@xxxxxxx> Subject: Re: [PATCH 0/4] Replace lseek..write/read to pwrite/pread Date: Wed, 30 Apr 2014 13:53:04 +0200 > On Wed, 30 Apr 2014 20:41:38 +0900 (JST) > HATAYAMA Daisuke <d.hatayama at jp.fujitsu.com> wrote: > >> From: Wang Nan <wangnan0 at huawei.com> >> Subject: [PATCH 0/4] Replace lseek..write/read to pwrite/pread >> Date: Sat, 26 Apr 2014 12:07:05 +0800 >> >> > In original code there are many operations read from /write to specific >> > positions of a file. This series of patches replace such patterns to >> > pread/pwrite calls, reduces more than 100 lines of code. >> > >> >> I'm now writing pthread support patch set and it will naturally >> include pread/pwrite like this patch set. >> >> It sounds to me that using pread/pwrite only to reduce lseek code is >> weak in motivation. Is there another visible merit? For example, any >> kind of performance improvement. I guess it's small even if exists >> compared to I/O. > > There is no user-visible benefit just from applying the patch, that's > right. > > The main benefit is that these pread/pwrite operations are atomic and do > not move the file offset, so all subprocesses (or threads) can share > the same file descriptor. This allows to remove reopen_dump_memory(), > for example. > > Anyway, is improving code readability really so weak argument? > > Petr T In the current code, parallelism occurs only when --split option is specified. It seems to me that reopen_dump_memory() is enough. So, it appears to me that this patch set just changes lseek(); read(); or lseek(); write() lines to pread() or pwrite(), so I don't see so big difference... -- Thanks. HATAYAMA, Daisuke
