Date: Sun, 05 Jun 2016 11:07:21 +0300 From: =?UTF-8?B?QnVsYXQgQnVsYXQ=?= <bltsrc@mail.ru> To: freebsd-hackers@freebsd.org Subject: =?UTF-8?B?VHVybnN0aWxlX3B1cnBvc2VfdHNfZnJlZQ==?= Message-ID: <1465114041.917499339@f133.i.mail.ru>
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Hi, guys. Have little question about implementation of turnstiles in the kernel. That is, what is the purpose of ts_free list in turnstile structure? Related file: kern/subr_turnstile.c I understand that turnstile is used for tracking non-sleepable locks, tracking blocked threads on that lock, that when thread blocks on lock it adds its own turnstile to lock's turnstile's ts_free list and regrabs any available turnstile from that lock's turnstile's ts_free list when it is waking up. Could you please explain, why algorithm does so, why goes through hassle of putting turnstile into ts_free only to regrab it from ts_free later, as it stores pointer to own turnstile and could keep it there, using only when it is the first thread to be blocked on a lock. There is definitely logic in using ts_free member, but it is a bit unclear for me. Would be glad to see your explanation, thanks. bnm
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