From: John Garry <john.garry@huawei.com> To: Cong Wang <xiyou.wangcong@gmail.com> Cc: <iommu@lists.linux-foundation.org>, LKML <linux-kernel@vger.kernel.org> Subject: Re: [Patch v2 2/3] iommu: optimize iova_magazine_free_pfns() Date: Mon, 2 Dec 2019 10:02:38 +0000 [thread overview] Message-ID: <9996d30c-e063-e74d-925f-4181c36ca764@huawei.com> (raw) In-Reply-To: <CAM_iQpX3MKoBRvxqc-bJ0HvASNeZmvVCYhbT53maMy-rqy4eiw@mail.gmail.com> On 30/11/2019 06:02, Cong Wang wrote: > On Fri, Nov 29, 2019 at 5:24 AM John Garry <john.garry@huawei.com> wrote: >> >> On 29/11/2019 00:48, Cong Wang wrote: >>> If the maganize is empty, iova_magazine_free_pfns() should >> >> magazine > > Good catch! > >> >>> be a nop, however it misses the case of mag->size==0. So we >>> should just call iova_magazine_empty(). >>> >>> This should reduce the contention on iovad->iova_rbtree_lock >>> a little bit. >>> >>> Cc: Joerg Roedel <joro@8bytes.org> >>> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> >>> --- >>> drivers/iommu/iova.c | 22 +++++++++++----------- >>> 1 file changed, 11 insertions(+), 11 deletions(-) >>> >>> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >>> index cb473ddce4cf..184d4c0e20b5 100644 >>> --- a/drivers/iommu/iova.c >>> +++ b/drivers/iommu/iova.c >>> @@ -797,13 +797,23 @@ static void iova_magazine_free(struct iova_magazine *mag) >>> kfree(mag); >>> } >>> >>> +static bool iova_magazine_full(struct iova_magazine *mag) >>> +{ >>> + return (mag && mag->size == IOVA_MAG_SIZE); >>> +} >>> + >>> +static bool iova_magazine_empty(struct iova_magazine *mag) >>> +{ >>> + return (!mag || mag->size == 0); >>> +} >>> + >>> static void >>> iova_magazine_free_pfns(struct iova_magazine *mag, struct iova_domain *iovad) >>> { >>> unsigned long flags; >>> int i; >>> >>> - if (!mag) >>> + if (iova_magazine_empty(mag)) >> >> The only hot path we this call is >> __iova_rcache_insert()->iova_magazine_free_pfns(mag_to_free) and >> mag_to_free is full in this case, so I am sure how the additional check >> helps, right? > > This is what I mean by "a little bit" in changelog, did you miss it or > misunderstand it? :) I was concerned that in the fastpath we actually make things very marginally slower by adding a check which will fail. Thanks, John > > Thanks. > . >
WARNING: multiple messages have this Message-ID (diff)
From: John Garry <john.garry@huawei.com> To: Cong Wang <xiyou.wangcong@gmail.com> Cc: iommu@lists.linux-foundation.org, LKML <linux-kernel@vger.kernel.org> Subject: Re: [Patch v2 2/3] iommu: optimize iova_magazine_free_pfns() Date: Mon, 2 Dec 2019 10:02:38 +0000 [thread overview] Message-ID: <9996d30c-e063-e74d-925f-4181c36ca764@huawei.com> (raw) In-Reply-To: <CAM_iQpX3MKoBRvxqc-bJ0HvASNeZmvVCYhbT53maMy-rqy4eiw@mail.gmail.com> On 30/11/2019 06:02, Cong Wang wrote: > On Fri, Nov 29, 2019 at 5:24 AM John Garry <john.garry@huawei.com> wrote: >> >> On 29/11/2019 00:48, Cong Wang wrote: >>> If the maganize is empty, iova_magazine_free_pfns() should >> >> magazine > > Good catch! > >> >>> be a nop, however it misses the case of mag->size==0. So we >>> should just call iova_magazine_empty(). >>> >>> This should reduce the contention on iovad->iova_rbtree_lock >>> a little bit. >>> >>> Cc: Joerg Roedel <joro@8bytes.org> >>> Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com> >>> --- >>> drivers/iommu/iova.c | 22 +++++++++++----------- >>> 1 file changed, 11 insertions(+), 11 deletions(-) >>> >>> diff --git a/drivers/iommu/iova.c b/drivers/iommu/iova.c >>> index cb473ddce4cf..184d4c0e20b5 100644 >>> --- a/drivers/iommu/iova.c >>> +++ b/drivers/iommu/iova.c >>> @@ -797,13 +797,23 @@ static void iova_magazine_free(struct iova_magazine *mag) >>> kfree(mag); >>> } >>> >>> +static bool iova_magazine_full(struct iova_magazine *mag) >>> +{ >>> + return (mag && mag->size == IOVA_MAG_SIZE); >>> +} >>> + >>> +static bool iova_magazine_empty(struct iova_magazine *mag) >>> +{ >>> + return (!mag || mag->size == 0); >>> +} >>> + >>> static void >>> iova_magazine_free_pfns(struct iova_magazine *mag, struct iova_domain *iovad) >>> { >>> unsigned long flags; >>> int i; >>> >>> - if (!mag) >>> + if (iova_magazine_empty(mag)) >> >> The only hot path we this call is >> __iova_rcache_insert()->iova_magazine_free_pfns(mag_to_free) and >> mag_to_free is full in this case, so I am sure how the additional check >> helps, right? > > This is what I mean by "a little bit" in changelog, did you miss it or > misunderstand it? :) I was concerned that in the fastpath we actually make things very marginally slower by adding a check which will fail. Thanks, John > > Thanks. > . > _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
next prev parent reply other threads:[~2019-12-02 10:02 UTC|newest] Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-11-29 0:48 [Patch v2 0/3] iommu: reduce spinlock contention on fast path Cong Wang 2019-11-29 0:48 ` Cong Wang 2019-11-29 0:48 ` [Patch v2 1/3] iommu: match the original algorithm Cong Wang 2019-11-29 0:48 ` Cong Wang 2019-11-29 14:43 ` John Garry 2019-11-29 14:43 ` John Garry 2019-11-30 5:58 ` Cong Wang 2019-11-30 5:58 ` Cong Wang 2019-12-02 10:55 ` John Garry 2019-12-02 10:55 ` John Garry 2019-12-03 19:26 ` Cong Wang 2019-12-03 19:26 ` Cong Wang 2019-12-02 16:58 ` Christoph Hellwig 2019-12-02 16:58 ` Christoph Hellwig 2019-12-03 19:24 ` Cong Wang 2019-12-03 19:24 ` Cong Wang 2019-11-29 0:48 ` [Patch v2 2/3] iommu: optimize iova_magazine_free_pfns() Cong Wang 2019-11-29 0:48 ` Cong Wang 2019-11-29 13:24 ` John Garry 2019-11-29 13:24 ` John Garry 2019-11-30 6:02 ` Cong Wang 2019-11-30 6:02 ` Cong Wang 2019-12-02 10:02 ` John Garry [this message] 2019-12-02 10:02 ` John Garry 2019-12-03 19:40 ` Cong Wang 2019-12-03 19:40 ` Cong Wang 2019-12-02 16:59 ` Christoph Hellwig 2019-12-02 16:59 ` Christoph Hellwig 2019-12-03 19:28 ` Cong Wang 2019-12-03 19:28 ` Cong Wang 2019-11-29 0:48 ` [Patch v2 3/3] iommu: avoid taking iova_rbtree_lock twice Cong Wang 2019-11-29 0:48 ` Cong Wang 2019-11-29 13:34 ` John Garry 2019-11-29 13:34 ` John Garry 2019-11-30 6:03 ` Cong Wang 2019-11-30 6:03 ` Cong Wang 2019-12-17 9:43 ` [Patch v2 0/3] iommu: reduce spinlock contention on fast path Joerg Roedel 2019-12-17 9:43 ` Joerg Roedel 2019-12-18 4:32 ` Cong Wang 2019-12-18 4:32 ` Cong Wang
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