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Date: Fri, 28 Mar 2008 17:53:16 -0700 (PDT) From: Linus Torvalds <torvalds@...ux-foundation.org> To: Roland McGrath <roland@...hat.com> cc: Andrew Morton <akpm@...ux-foundation.org>, Martin Schwidefsky <schwidefsky@...ibm.com>, linux-s390@...r.kernel.org, tony.luck@...el.com, linux-ia64@...r.kernel.org, linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 2/4] set_restore_sigmask TIF_SIGPENDING On Fri, 28 Mar 2008, Roland McGrath wrote: > > Set TIF_SIGPENDING in set_restore_sigmask. This lets arch code take > TIF_RESTORE_SIGMASK out of the set of bits that will be noticed on > return to user mode. On some machines those bits are scarce, and we > can free this unneeded one up for other uses. Hmm. That probably means that TIF_RESTORE_SIGMASK shouldn't be a "TIF" flag at all, but a "TS" ("thread status") flag. The TS flags are faster, because they are thread-synchronous and do not need atomic accesses (ie they are purely thread-local in setting, testing and clearing). Of course, it may well not be worth it. Unlike the TIF flags, the TS flags have been architecture-specific and I don't think all architectures even do them (x86 uses them for FP state bits and stuff like that). I guess TIF_RESTORE_SIGMASK is never *so* performance-critical that we'd care about the difference between a single cycle (approx) for a non-atomic "or" into memory and an atomic bitop (~50 cycles or so). Linus -- 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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