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Date: Fri, 7 Dec 2007 14:55:05 +0300 From: Evgeniy Polyakov <johnpol@....mipt.ru> To: Zach Brown <zach.brown@...cle.com> Cc: linux-kernel@...r.kernel.org, Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...e.hu>, Ulrich Drepper <drepper@...hat.com>, Arjan van de Ven <arjan@...radead.org>, Andrew Morton <akpm@....com.au>, Alan Cox <alan@...rguk.ukuu.org.uk>, "David S. Miller" <davem@...emloft.net>, Suparna Bhattacharya <suparna@...ibm.com>, Davide Libenzi <davidel@...ilserver.org>, Jens Axboe <jens.axboe@...cle.com>, Thomas Gleixner <tglx@...utronix.de>, Dan Williams <dan.j.williams@...il.com>, Jeff Moyer <jmoyer@...hat.com>, Simon Holm Thogersen <odie@...aau.dk>, suresh.b.siddha@...el.com Subject: Re: [PATCH 5/6] syslets: add generic syslets infrastructure Hi Zach. On Thu, Dec 06, 2007 at 03:20:18PM -0800, Zach Brown (zach.brown@...cle.com) wrote: > +/* > + * XXX todo: > + * - do we need all this '*cur = current' nonsense? > + * - try to prevent userspace from submitting too much.. lazy user ptr read? > + * - explain how to deal with waiting threads with stale data in current > + * - how does userspace tell that a syslet completion was lost? > + * provide an -errno argument to the userspace return function? > + */ > + > +/* > + * These structs are stored on the kernel stack of tasks which are waiting to > + * return to userspace. They are linked into their parent's list of syslet > + * children stored in 'syslet_tasks' in the parent's task_struct. > + */ > +struct syslet_task_entry { > + struct task_struct *task; > + struct list_head item; > +}; > + > +/* > + * syslet_ring doesn't have any kernel-side storage. Userspace allocates them > + * in their address space and initializes their fields and then passes them to > + * the kernel. > + * > + * These hashes provide the kernel-side storage for the wait queues which > + * sys_syslet_ring_wait() uses and the mutex which completion uses to serialize > + * the (possible blocking) ordered writes of the completion and kernel head > + * index into the ring. > + * > + * We chose the bucket that supports a given ring by hashing a u32 that > + * userspace sets in the ring. > + */ > +#define SYSLET_HASH_BITS (CONFIG_BASE_SMALL ? 4 : 8) > +#define SYSLET_HASH_NR (1 << SYSLET_HASH_BITS) > +#define SYSLET_HASH_MASK (SYSLET_HASH_NR - 1) > +static wait_queue_head_t syslet_waitqs[SYSLET_HASH_NR]; > +static struct mutex syslet_muts[SYSLET_HASH_NR]; Why do you care about hashed tables scalability and not using trees? -- Evgeniy Polyakov -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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